So if you’re an iOS developer, you should also learn to prioritize security at every stage of app development.

Swift, Apple’s modern programming language, offers a wealth of tools and frameworks that simplify development while enhancing security, but only when used correctly.

This article explores 10 common security pitfalls in Swift-based iOS apps and offers practical strategies to mitigate them.

Prerequisites

Before diving in, you’ll need:

• Working knowledge of Swift and iOS development.

• Access to Xcode.

• Basic understanding of how iOS apps communicate with servers.

• Familiarity with Terminal/command line basics.

The code examples are practical and explained step-by-step, making them accessible to junior developers while still offering value to experienced ones looking to strengthen their app's security.

What we’ll cover:

• What are the Most Prevalent Security Traps in Swift iOS Applications?
  • 1. Insecure Data Storage
  • 2. Weak Network Communication
  • 3. Improper Input Validation
  • 4. Hardcoding Secrets
  • 5. Insufficient Authentication and Authorization
  • 6. Insecure Logging and Error Handling
  • 7. Ignoring Code Obfuscation and Reverse Engineering
  • 8. Insecure Third-Party Libraries
  • 9. Insufficient Biometric and Multi-Factor Authentication
  • 10. Disregarding Periodic Security Testing

What are the Most Prevalent Security Traps in Swift iOS Applications?

Swift and iOS offer robust security features, but mistakes still happen. Following are the most common traps and how to fix them:

1. Insecure Data Storage

Among the most common mistakes developers make is having sensitive data stored insecurely. Passwords, tokens, or even individual user data can be left by accident in UserDefaults or local storage in unencrypted form.

While UserDefaults is convenient for small amounts of data, it is not secure for sensitive data as it is so easily accessible to attackers if the device is compromised.

How to Fix:

Use the Keychain Services API to securely store sensitive data. Keychain encrypts data and binds it to the device so that it can't be accessed by other unauthorized applications or users.

You can securely store credentials using libraries in Swift such as KeychainAccess or the built-in SecItemAdd and SecItemCopyMatching functions.

For example, this how you can store a user password in Keychain so as to ensure sensitive data is stored securely:

do {

try keychain.set("userPassword123", key: "userPassword")

} catch {

    print("Error saving to Keychain: \(error)")

}

Behind the scenes, here’s what happens when you call keychain.set("userPassword123", key: "userPassword") inside a KeychainManager class that uses Apple’s native Security framework for storage:

import Security

class KeychainManager {
 func set(_ value: String, key: String) throws {
     // 1. Convert string to Data
     guard let data = value.data(using: .utf8) else {
         throw NSError(domain: "KeychainManager", code: -1)
     }

     // 2. Build the query dictionary
     let query: [String: Any] = [
         // Store as password
         kSecClass as String: kSecClassGenericPassword,
         // Your app's bundle identifier
         kSecAttrService as String: "com.yourapp.keychain",
         // "userPassword"
         kSecAttrAccount as String: key,
         // "userPassword123" encrypted
         kSecValueData as String: data,
         kSecAttrAccessible as String: kSecAttrAccessibleAfterFirstUnlock
     ]
     // 3. Save to keychain (iOS encrypts it automatically)
     let status = SecItemAdd(query as CFDictionary, nil)
     // 4. Check if successful
     guard status == errSecSuccess else {
         throw NSError(domain: "KeychainManager", code: Int(status))
     }
 }
}

When this function runs, iOS converts the string value, such as "userPassword123", into encrypted binary data and stores it securely in the device’s Keychain database. The entry is saved under the provided key (for example, "userPassword"), and only your app can access it.

Behind the scenes, the Keychain leverages strong security features, including hardware-backed encryption using device-specific keys, optional biometric protection through Face ID or Touch ID, and app-level isolation to ensure that no other app can read or modify your stored credentials.

2. Weak Network Communication

Transmitting sensitive data over the network is another area prone to vulnerabilities. Using unencrypted HTTP connections exposes your app to man-in-the-middle (MITM) attacks, allowing attackers to intercept and modify data in transit.

The Problem: When data travels between your app and server over an insecure connection, attackers on the same network (like public Wi-Fi) can:

• Read sensitive information (passwords, personal data, payment details)

• Modify requests and responses

• Impersonate your legitimate server

How to Fix:

1. Always Use HTTPS
HTTPS encrypts all data in transit, making it unreadable to attackers. iOS's App Transport Security (ATS) enforces this by blocking insecure HTTP connections by default:

// ❌ INSECURE - HTTP connection (blocked by ATS by default)
let url = URL(string: "http://api.example.com/login")

// ✅ SECURE - HTTPS connection
let url = URL(string: "https://api.example.com/login")

You’ll want to avoid adding ATS exceptions to your Info.plist unless absolutely necessary. If a third-party API only supports HTTP, contact them to upgrade or find a more secure alternative.

2. Implement Certificate Pinning (Advanced Protection)

Even with HTTPS, your app could still be vulnerable to sophisticated MITM attacks. An attacker could install a fraudulent certificate on a user's device (through malware or social engineering), for example, and intercept HTTPS traffic that appears valid. The attacker's fake certificate would be trusted by the device, allowing them to decrypt and read "secure" communications.

Certificate pinning solves this by making your app trust only your specific server's certificate, rejecting all others – even if they're otherwise valid.

How Certificate Pinning Works:

Your app stores the expected certificate (or its public key hash) and validates it during each connection:

class SecureNetworkManager: NSObject, URLSessionDelegate {

    // Store your server's certificate hash
    // Get this by running: openssl x509 -in certificate.crt -pubkey -noout | openssl pkey -pubin -outform der | openssl dgst -sha256 -binary | base64
    private let expectedPublicKeyHash = "YOUR_CERTIFICATE_HASH_HERE"

    func urlSession(
        _ session: URLSession,
        didReceive challenge: URLAuthenticationChallenge,
        completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void
    ) {
        // Step 1: Check if this is a server trust challenge (certificate validation)
        guard challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust,
              let serverTrust = challenge.protectionSpace.serverTrust
        else {
            // Not a certificate challenge; use default handling
            completionHandler(.performDefaultHandling, nil)
            return
        }

        // Step 2: Validate that the server's certificate matches our pinned certificate
        if isValidServerTrust(serverTrust) {
            // Certificate matches - proceed with the connection
            completionHandler(.useCredential, URLCredential(trust: serverTrust))
        } else {
            // Certificate doesn't match - reject the connection to prevent MITM attack
            completionHandler(.cancelAuthenticationChallenge, nil)
        }
    }

    // Validates the server's certificate against our pinned hash
    private func isValidServerTrust(_ serverTrust: SecTrust) -> Bool {
        // Extract the server's certificate
        guard let serverCertificate = SecTrustGetCertificateAtIndex(serverTrust, 0) else {
            return false
        }

        // Get the public key from the certificate
        let serverPublicKey = SecCertificateCopyKey(serverCertificate)
        guard let publicKey = serverPublicKey else {
            return false
        }

        // Convert the public key to data and hash it
        var error: Unmanaged<CFError>?
        guard let publicKeyData = SecKeyCopyExternalRepresentation(publicKey, &error) as Data? else {
            return false
        }

        // Hash the public key using SHA-256
        let publicKeyHash = SHA256.hash(data: publicKeyData)
        let publicKeyHashString = Data(publicKeyHash).base64EncodedString()

        // Compare with our expected hash
        return publicKeyHashString == expectedPublicKeyHash
    }
}

What this code does, step-by-step:

1. urlSession(_:didReceive:completionHandler:) – This method is called whenever your app makes an HTTPS connection. iOS asks: "Should I trust this server's certificate?"

2. Check authentication method – We verify this is a server trust challenge (certificate validation), not some other type of authentication.

3. Validate the certificate – We call isValidServerTrust(), which:

   • Extracts the server's certificate from the connection

   • Gets the public key from that certificate

   • Hashes the public key using SHA-256

   • Compares the hash to our stored, expected hash

4. Make a decision:

• If hashes match, then the server is legitimate. Proceed with .useCredential.

• If hashes don't match, we have a potential MITM attack. Cancel with .cancelAuthenticationChallenge.

So how does this prevent MITM attacks? Even if an attacker installs a fraudulent certificate on the user's device and intercepts traffic, their certificate's hash won't match your pinned hash. Your app will reject the connection, preventing the attacker from decrypting your traffic.

3. Additional Protection: Recommend a VPN on Public Wi-Fi

You can also recommend that users connect through a VPN when on public Wi-Fi for an added layer of security, and provide guidance on how to use a VPN effectively to keep their data safe.

For developers, maintaining strong app security also depends on having a well-optimized system, learning how to speed up a slow Mac can help ensure smoother builds, faster testing, and a more secure overall development workflow.

3. Improper Input Validation

Some developers neglect correct input validation, leading to a number of vulnerabilities including SQL injection, remote code execution, and data corruption.

While Swift has strong typing support, some developers don’t sanitize user input or API responses. Incorporating real-time API email validation ensures that users provide legitimate, properly formatted email addresses before they are stored or processed, reducing both security risks and data quality issues.

How to Fix:

Input validation is your first line of defense against malicious data. Here's how to protect your iOS applications:

1. Validate User Input with Patterns

Always validate user input using regular expressions or predefined patterns before processing. For example, when accepting email addresses:

func isValidEmail(_ email: String) -> Bool {
    let emailRegex = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,64}"
    let emailPredicate = NSPredicate(format: "SELF MATCHES %@", emailRegex)
    return emailPredicate.evaluate(with: email)
}

// Only accept properly formatted data
guard isValidEmail(userEmail) else {
    // Reject invalid input
    return
}

This ensures that only properly formatted data is accepted, preventing malformed or malicious input from entering your system.

2. Sanitize API Responses

Never trust external data. Always validate and sanitize API responses before using them:

if let userAge = apiResponse["age"] as? Int,
   userAge >= 0 && userAge <= 150 {
    // Safe to use
    user.age = userAge
} else {
    // Handle invalid data appropriately
    throw ValidationError.invalidAge
}

3. Use Parameterized Queries (Most Critical)

The most dangerous mistake is building database queries through string concatenation. Consider this vulnerable code:

// ❌ NEVER DO THIS - Vulnerable to SQL Injection
let username = userInput  // Could be: "admin' OR '1'='1"
let query = "SELECT * FROM users WHERE username = '\(username)'"
database.execute(query)

If a malicious user enters admin' OR '1'='1 as their username, the query becomes:

SELECT * FROM users WHERE username = 'admin' OR '1'='1'

This would return all users in the database instead of just one, potentially exposing sensitive data. The secure solution uses parameterized queries:

// ✅ SAFE - Using parameterized queries
let query = "SELECT * FROM users WHERE username = ?"
database.execute(query, withArgumentsIn: [username])

In this approach, the ? is a placeholder that the database treats as a parameter, not as part of the SQL command. The username value is passed separately in the withArgumentsIn array.

This means that even if a user tries to inject SQL code like admin' OR '1'='1, the database will treat the entire string as a literal username to search for – not as executable SQL code. The database engine automatically escapes any special characters, completely eliminating the risk of SQL injection.

By separating the query structure from the data, parameterized queries ensure that user input can never alter the intended logic of your SQL statements.

4. Hardcoding Secrets

API keys, credentials, or private tokens hard-coded in the source code is another serious security mistake. Attackers can extract such secrets from compiled binaries using reverse-engineering tools, especially for apps released to the public.

Once exposed, these credentials can be used to access your backend services, potentially leading to data breaches or unauthorized charges.

The Problem – Hardcoded Secrets:

// NEVER DO THIS
class APIClient {
    private let apiKey = "1234567890abcdef"
    private let secretToken = "sk_live_51H..."

    func makeRequest() {
        // These secrets are embedded in your binary
        let headers = ["Authorization": "Bearer \(apiKey)"]
    }
}

How to Fix:

Never store sensitive credentials directly in your code. Here are secure alternatives:

Solution 1: Fetch Secrets from Backend at Runtime

The most secure approach is to never store secrets on the client at all. Instead, authenticate users and let your backend make authorized API calls:

class APIClient {
    private var sessionToken: String?

    // User logs in and receives a temporary session token
    func authenticateUser(email: String, password: String) async throws {
        let response = try await backend.login(email: email, password: password)
        // Store only a temporary, user-specific session token
        self.sessionToken = response.sessionToken
    }

    // Backend handles the actual API calls with the real API key
    func fetchUserData() async throws -> UserData {
        guard let token = sessionToken else {
            throw AuthError.notAuthenticated
        }

        // Your backend receives this request, validates the session token,
        // then uses its own API keys to fetch data from third-party services
        return try await backend.getUserData(sessionToken: token)
    }
}

How this works:

Your app never knows the actual API keys. When a user needs data, your app sends a request to your own backend server with a session token. Your backend validates the token, then uses its own securely stored API keys to make the actual third-party API calls. This way, the real secrets never leave your server.

Solution 2: Environment Variables or Config Files (Development Only)

For development environments, use .xcconfig files that are excluded from version control:

// Secrets.xcconfig (add to .gitignore!)
API_KEY = your_dev_api_key_here
API_SECRET = your_dev_secret_here

// Access in your code through Info.plist
class Config {
    static let apiKey: String = {
        guard let key = Bundle.main.object(forInfoDictionaryKey: "API_KEY") as? String else {
            fatalError("API_KEY not found in configuration")
        }
        return key
    }()
}

Important: This approach is only suitable for non-production environments! Never ship production API keys with your app, even in config files.

5. Insufficient Authentication and Authorization

Relying on client-side authentication and authorization checks is risky. Attackers can cause the app to bypass these checks and access in an unauthorized way by brute forcing or tampering with the app/runtime.

How to Fix:

• Do authentication and authorization on the server side instead of the client-side.

• Use JWT (JSON Web Tokens) or OAuth 2.0 for authenticated user login.

• Token expiration and refresh logic needs to be implemented in order to minimize the likelihood of token theft.

Example: Securely sending JWT:

let request = URLRequest(url: apiURL)

request.setValue("Bearer \(jwtToken)", forHTTPHeaderField: "Authorization")

6. Insecure Logging and Error Handling

Extensive and insecure logging practices, as well as uncaught exceptions, can lead to the exposure of sensitive information including usernames, passwords, and API keys.

How to Fix:

• Log sensitive information carefully.

• Implement controlled error management and provide the minimum amount of information in user-presented messages.

• Implement secure logging libraries that mask or encrypt personal data.

do {
    try someRiskyOperation()
} catch {
    // Log error securely
    Logger.log("Operation failed: \(error.localizedDescription)")
}

7. Ignoring Code Obfuscation and Reverse Engineering

Swift binaries can be reverse-engineered to expose sensitive business logic, algorithms, or hidden secrets. Attackers use tools like Hopper Disassembler, class-dump, or IDA Pro to decompile your app and analyze how it works internally. This risk is often underestimated, especially for smaller apps, but any app can be a target.

This means that when you compile a Swift app, the resulting binary contains:

• Class names and method signatures

• String literals (URLs, error messages, keys)

• The structure of your code logic

• Algorithm implementations

An attacker can extract this information and use it to understand your app's authentication flow and bypass it, copy your proprietary algorithms, find hardcoded API endpoints or keys you thought were "hidden", discover premium features to unlock without paying, and so on.

Why It's Bad – Real Example:

Let's imagine you have a premium feature check in your app:

class FeatureManager {
    func isPremiumUser() -> Bool {
        // Check if user has premium access
        let hasSubscription = UserDefaults.standard.bool(forKey: "premium_unlocked")
        return hasSubscription
    }

    func unlockPremiumFeature() {
        guard isPremiumUser() else {
            showPaywall()
            return
        }
        // Show premium content
        showPremiumContent()
    }
}

An attacker could reverse-engineer your app and discover that the method isPremiumUser() controls access, and that it simply checks a UserDefaults key called premium_unlocked. They would then know that they could use runtime manipulation tools to set this value to true, bypassing your paywall entirely.

How to Fix:

1. Use Swift Compiler Optimizations

Enable optimization flags that strip debugging symbols and make the binary harder to read:

// In your build settings:
// - Set "Optimization Level" to "-O" (or -Osize) for release builds
// - Enable "Strip Debug Symbols During Copy" = YES
// - Set "Strip Style" to "All Symbols"

This removes function names and makes the compiled code less readable – though class/method names remain partially visible.

2. Use Symbol Obfuscation Tools

Tools like SwiftShield can rename your classes, methods, and properties to meaningless names:

// Before obfuscation (readable to attackers):
class FeatureManager {
    func isPremiumUser() -> Bool { ... }
}

// After obfuscation (harder to understand):
class a7f3b2 {
    func x9k2m() -> Bool { ... }
}

While this doesn't prevent reverse engineering, it makes it significantly harder for attackers to understand what the code does.

3. Move Sensitive Logic to the Server (Best Practice)

Instead of checking premium status locally, verify it server-side:

// ✅ Secure approach - Server validates everything
class FeatureManager {
    func unlockPremiumFeature() async {
        do {
            // Server checks if user truly has premium access
            let hasAccess = try await backend.verifyPremiumAccess(userId: currentUserId)

            if hasAccess {
                showPremiumContent()
            } else {
                showPaywall()
            }
        } catch {
            // Handle error
            showPaywall()
        }
    }
}

How this works:

Your backend maintains the source of truth about premium access. Even if an attacker reverse-engineers your app and tries to bypass the check, the server will reject unauthorized requests. The app becomes just a UI layer, while all critical decisions happen server-side – where attackers can't manipulate them.

The key principle is to assume your app code is public: never rely on client-side checks for security-critical operations like payments, access control, or authentication. Use obfuscation to make reverse engineering harder, but ultimately move sensitive logic to your secure backend

8. Insecure Third-Party Libraries

Third-party libraries are at risk if they are hacked or outdated. Developers might inadvertently prioritize app functionality over potential security risks from dependencies, and ETL tools can further help by streamlining the monitoring and processing of dependency-related data to identify vulnerabilities more efficiently.

On a broader scale, implementing strong data center security practices ensures that even if third-party components introduce risks, the underlying infrastructure remains resilient against attacks.

How to Fix:

• Use only high-quality, well-maintained libraries.

• Update dependencies and monitor CVEs (Common Vulnerabilities and Exposures).

• Audit library code if it handles sensitive data.

9. Insufficient Biometric and Multi-Factor Authentication

Most applications rely on passwords alone, which are vulnerable to being hacked. Enabling biometrics like Face ID or Touch ID enhances security for users.

How to Fix:

• Tie LocalAuthentication framework for biometric authentication.

• Combine biometrics with server-based authentication for multifactor authentication (MFA).

import LocalAuthentication

let context = LAContext()

var error: NSError?

if context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) {

    context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics,

                        localizedReason: "Access your account") { success, authError in

        DispatchQueue.main.async {

         if success {

                // Proceed securely

         } else {

                // Handle failure (authError may contain the reason)

                print("Authentication failed: \(authError?.localizedDescription ?? "Unknown error")")

         }

     }

}

} else {

// Biometrics not available, check error for details

    print("Biometrics unavailable: \(error?.localizedDescription ?? "Unknown error")")

}

10. Disregarding Periodic Security Testing

Apps, despite following best practices during development, often contain unexplored vulnerabilities that emerge from complex interactions, third-party dependencies, or newly discovered attack vectors. Regular security testing is absolutely essential to discover these vulnerabilities before attackers exploit them.

Security testing should happen at multiple stages, using accessible tools and practices:

1. Automated security scans: Run automatically with every build to catch common issues.

2. Self-conducted code audits: Regular security-focused reviews of your own code using established guidelines.

3. Vulnerability scanning tools: Use free tools like MobSF to analyze your app for security flaws.

4. Dependency audits: Checking third-party libraries for known security vulnerabilities.

How to Fix:

1. Implement Automated Security Scans in CI/CD

Integrate security scanning tools into your continuous integration pipeline so every code change is automatically checked:

# Example: GitHub Actions workflow for automated security scanning
name: Security Scan

on: [push, pull_request]

jobs:
  security-scan:
    runs-on: macos-latest

    steps:
      - name: Checkout code
        uses: actions/checkout@v3

      - name: Run MobSF Security Scan
        run: |
          # Mobile Security Framework - scans for common vulnerabilities
          docker run -v $(pwd):/app opensecurity/mobile-security-framework-mobsf

      - name: Dependency Vulnerability Check
        run: |
          # Check CocoaPods/SPM dependencies for known CVEs
          brew install dependency-check
          dependency-check --scan ./Podfile.lock --format JSON

      - name: Secret Detection
        run: |
          # Detect accidentally committed secrets
          brew install truffleHog
          truffleHog filesystem . --json

      - name: Fail build on critical issues
        run: |
          if grep -q "CRITICAL" security-report.json; then
            echo "Critical security issues found!"
            exit 1
          fi

Automated scans check for:

• Hardcoded API keys, tokens, or passwords

• Insecure network configurations (allowing HTTP instead of HTTPS)

• Weak cryptographic algorithms

• Known vulnerabilities in third-party libraries

• Improper SSL/TLS certificate validation

• Insecure data storage (storing sensitive data in UserDefaults)

• Excessive app permissions

Example output from an automated scan:

Security Scan Results:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
[CRITICAL] Hardcoded API Key Found
  File: APIClient.swift:15
  Issue: API key "sk_live_abc123..." detected in source code

[HIGH] Insecure HTTP Connection
  File: NetworkManager.swift:42
  Issue: App allows cleartext HTTP traffic to api.example.com
  Fix: Enforce HTTPS or add exception to Info.plist if required

[MEDIUM] Weak Encryption Algorithm
  File: DataEncryption.swift:28
  Issue: Using MD5 for hashing (cryptographically broken)
  Fix: Use SHA-256 or better

[LOW] Outdated Dependency
  Library: Alamofire 4.2.0
  Issue: Known vulnerability CVE-2021-12345
  Fix: Update to version 5.6.0 or later
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Build Failed: 2 critical issues must be fixed before deployment

2. Use MobSF (Mobile Security Framework) for Vulnerability Analysis

MobSF is a free, automated tool that analyzes your iOS app for security issues:

# Install and run MobSF locally
docker pull opensecurity/mobile-security-framework-mobsf
docker run -it -p 8000:8000 opensecurity/mobile-security-framework-mobsf

# Upload your .ipa file through the web interface at localhost:8000
# MobSF will analyze and provide a detailed security report

What MobSF checks:

• Binary analysis for hardcoded secrets

• Insecure data storage patterns

• Weak cryptographic implementations

• Insecure network connections

• Code quality and security best practices

• Compliance with security standards

3. Conduct Regular Code Audits Using OWASP MSTG

Use the OWASP Mobile Security Testing Guide as a checklist to audit your own code:

// Example: Following OWASP MSTG recommendations for secure storage
class SecureStorage {
    // ❌ Insecure - UserDefaults is not encrypted
    func saveTokenInsecurely(_ token: String) {
        UserDefaults.standard.set(token, forKey: "authToken")
    }

    // ✅ Secure - Using Keychain as OWASP recommends
    func saveTokenSecurely(_ token: String) throws {
        let data = token.data(using: .utf8)!
        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrAccount as String: "authToken",
            kSecValueData as String: data,
            kSecAttrAccessible as String: kSecAttrAccessibleWhenUnlockedThisDeviceOnly
        ]

        SecItemDelete(query as CFDictionary)
        let status = SecItemAdd(query as CFDictionary, nil)

        guard status == errSecSuccess else {
            throw StorageError.saveFailed
        }
    }
}

OWASP MSTG Checklist for Self-Audit:

• [ ] Are all sensitive data encrypted at rest?

• [ ] Is HTTPS enforced for all network calls?

• [ ] Are certificates properly validated?

• [ ] Is sensitive data excluded from logs?

• [ ] Are API keys and secrets not hardcoded?

• [ ] Is user input validated and sanitized?

• [ ] Are authentication tokens stored securely in Keychain?

4. Automated Dependency Scanning

Monitor your dependencies continuously for newly discovered vulnerabilities:

# For CocoaPods projects
gem install cocoapods-audit
pod audit

# For Swift Package Manager
# Use GitHub Dependabot (free for public repos) or
brew install swift-outdated
swift-outdated

And set up automated alerts with these tools:

• GitHub Dependabot: Automatically creates PRs when vulnerable dependencies are detected (free)

• Snyk: Free tier available for open-source projects

• OWASP Dependency-Check: Free command-line tool

Conclusion

Developing secure iOS apps using Swift is all about forward-thinking. You should do all you can to avoid these common errors, like insecure storage of data, poor network communication, hard-coded secrets, or poor authentication.

Using Keychain for confidential information, requiring HTTPS, input validation, and multifactor authentication are all steps that decrease risk.

Regular testing for security vulnerabilities and limiting third-party library use can also further enhance your app's security.

Security is a continuous responsibility. Swift provides tools, but the developers need to apply those tools carefully. Security being tackled right from the start protects users' information, creates trust, and protects the reputation of the application.

With the release of Swift 6 and its new Embedded Swift compilation mode, developers now have access to a modern, memory-safe, and performant alternative that’s tailored specifically for resource-constrained systems.

While languages like Rust have also emerged to address these issues, Embedded Swift brings the clarity and safety of Swift to microcontroller environments, without giving up on determinism, binary size, or hardware access.

This article introduces Embedded Swift and explores how it compares to traditional C/C++ development. We’ll cover its key features, programming and memory models, how to set up the toolchain for STM32 microcontrollers, and how to link Swift with existing C drivers.

Along the way, we’ll examine performance trade-offs, growing ecosystem support, and the broader industry movement toward memory-safe languages. As I hope you’ll see, Swift is a serious contender in the future of embedded development.

Prerequisites

To get the most out of this article, you should have a basic understanding of programming in Swift and C. Familiarity with embedded hardware platforms and firmware development concepts will also be helpful.

If you're new to embedded systems, consider reviewing this introductory guide to embedded firmware to build foundational knowledge before diving into Embedded Swift.

Scope

This article is intended as a practical introduction to Embedded Swift. It covers:

• An overview of Embedded Swift and its key language features

• Swift’s programming and memory model in an embedded context

• Setting up the Embedded Swift toolchain on macOS for STM32 microcontrollers

• Interoperability with C code and linking to existing low-level drivers

• A look at memory and instruction-level performance

• Future directions and use cases for Embedded Swift

Note that this article does not provide a full tutorial on the Swift language itself. While the primary focus is on STM32, similar principles apply to other supported platforms such as ESP32, Raspberry Pi Pico, and nRF52.

Table of Contents:

• What is Swift? What is Embedded Swift?

• Swift Programming Model

• Swift Memory Management

• Memory and Instruction Cycle Comparison

• How to Setup Embedded Swift

• C-Swift Linkages:

• Future Work

• Conclusion

What is Swift? What is Embedded Swift?

Swift is a modern programming language developed by Apple that combines the performance of compiled languages with the expressiveness and safety of modern language design. While Swift was originally created for iOS and macOS development, it has evolved into a powerful general-purpose language used in server-side development, systems programming, and increasingly, embedded systems.

Embedded Swift is a special compilation mode introduced in Swift 6 that brings the benefits of Swift to resource-constrained platforms like microcontrollers. It lets developers use a safe, high-level language while still producing compact, deterministic, and performant binaries suitable for embedded applications.

Key Features of Swift

Embedded Swift retains many of the powerful language features that make Swift an attractive alternative to C/C++ in embedded development:

Type Safety: Swift uses a strong static type system, which prevents many programming errors at compile time. Unlike C, where type mismatches can result in undefined behavior, Swift ensures all types are used correctly before code even runs.

Strict Type Checking: Swift doesn't allow implicit type conversions that could lose data or cause unexpected behavior. For example:

// This won't compile in Swift
let integer: Int = 42
let decimal: Double = 3.14
let result = integer + decimal  // Error: Cannot convert value of type 'Int' to expected argument type 'Double'

// You must be explicit about conversions
let result = Double(integer) + decimal  // Correct

Non-nullable Types by Default: In C, pointers can be null by default, which introduces risk. In Swift, variables cannot be nil unless explicitly marked as optionals:

var name: String = "John"
name = nil  // Compile error - String cannot be nil

var optionalName: String? = "John"
optionalName = nil  // This is allowed

Memory Safety via ARC (Covered in detail later):

Swift manages memory automatically using Automatic Reference Counting (ARC). Unlike manual memory management in C/C++, ARC handles object lifecycles efficiently without unpredictable garbage collection pauses. We'll cover ARC and its impact in embedded contexts in a dedicated section later.

Modern Syntax:
Swift's syntax is clean, consistent, and designed for readability. It supports modern paradigms including:

• Functional programming (map, filter, reduce)

• Generics (type-safe abstractions)

• Protocol-Oriented Programming (discussed in the next section)

These features allow you to write more expressive and maintainable code compared to procedural C or inheritance-heavy C++.

Performance:
Swift is designed to perform on par with C++ in many scenarios. Optimizations such as inlining, dead code elimination, and static dispatch help ensure that high-level abstractions don’t compromise performance. In embedded mode, Swift disables features like runtime reflection and dynamic dispatch to further reduce overhead.

To fully leverage Swift for embedded development, it's important to understand its programming model. Unlike C’s procedural approach or C++’s class-heavy design, Swift promotes protocol-oriented programming and composition, which offers both flexibility and safety in embedded system design.

Swift Programming Model

Swift embraces a multi-paradigm programming model that blends object-oriented, functional, and protocol-oriented programming, all underpinned by strong type safety and memory safety.

For embedded developers coming from C or C++, this model may feel different at first. But it provides a more modular and testable way to build complex systems, something especially valuable in embedded applications where hardware abstraction and strict reliability are critical.

Protocol-Oriented Programming (POP)

Swift emphasizes protocols over inheritance, encouraging developers to define behaviors through protocols and implement them using value types like struct and enum, rather than relying heavily on classes.

This philosophy favors composition over inheritance, allowing you to build complex functionality by combining smaller, well-defined components.

Key Concepts:

• protocol defines required behavior.

• Protocol extensions provide default behavior.

• Prefer value semantics using struct.

Example:

protocol Speakable {
    func speak()
}

extension Speakable {
    func speak() {
        print("Default sound")
    }
}

struct Dog: Speakable {
    func speak() {
        print("Woof!")
    }
}

Embedded Swift uses protocols with static dispatch. With static dispatch, the compiler knows the exact memory address of the function to call and can generate a direct jump instruction. There's no runtime lookup, no indirection, and no uncertainty.

Why POP Matters for Embedded Systems

First, you get flexible hardware extraction. Protocols make it easy to define interfaces for hardware components, allowing for mock implementations during testing or platform-specific variations.

Second, you have nice low overhead. Embedded Swift uses static dispatch for protocols, meaning there’s no runtime lookup, and calls are resolved at compile time for maximum performance.

Also, struct and enum types avoid heap allocations, making code more efficient and predictable in low-memory environments.

Now that we’ve explored how Swift’s programming model enables safer and more modular embedded code, let’s turn to another critical piece of the puzzle: memory management. Swift’s use of Automatic Reference Counting (ARC) replaces manual memory handling and offers important benefits, and tradeoffs, for embedded systems.

Swift Memory Management

One of Swift’s most impactful features, especially in the context of embedded systems, is its use of Automatic Reference Counting (ARC) for memory management. Unlike C/C++, where memory must be manually allocated and freed using malloc and free, Swift automates this process while maintaining deterministic performance.

This automation significantly reduces the risk of common memory-related bugs like leaks, dangling pointers, or use-after-free errors, all of which are notorious in low-level C code.

How ARC works

Swift supports ARC not only for the Cocoa Touch API's but for all APIs, providing a streamlined approach to memory management. Unlike garbage collection systems that can cause unpredictable pauses, ARC works deterministically at compile time and runtime to manage memory.

ARC automatically tracks and manages the lifetime of objects in memory based on how many references point to them.

• Reference Counting: Every object has a counter that tracks how many strong references point to it.

• Retain / Release: The compiler inserts retain and release calls automatically during assignment and deinitialization.

• Immediate Deallocation: When the reference count reaches zero, the object is deallocated immediately.

• Deterministic: Unlike garbage collectors, ARC doesn’t introduce unpredictable pauses or runtime scanning.

Swift offers multiple reference types to give you precise control over memory behavior and prevent cycles:

Strong References (default)

• Keeps the referenced object alive.

• Used in most cases.

class MotorController {
    var sensor: SensorData?  // Strong reference

    func updateReading(newData: SensorData) {
        self.sensor = newData  // Previous sensor data automatically deallocated
    }
}

Weak References

• Used to break reference cycles (especially in two-way object relationships).

• Automatically becomes nil when the referenced object is deallocated.

class Device {
    var controller: MotorController?

    deinit {
        print("Device deallocated")
    }
}

class MotorController {
    weak var device: Device?  // ← Weak reference breaks the cycle

    deinit {
        print("MotorController deallocated")
    }
}

func breakCycle() {
    let device = Device()
    let controller = MotorController()

    device.controller = controller
    controller.device = device  // ← This is now a weak reference

    // When this function ends, both objects are properly deallocated
}

breakCycle()
// Output:
// Device deallocated
// MotorController deallocated

Unowned References

• Non-optional version of weak.

• Assumes the object will never be deallocated while still in use.

• More lightweight than weak, but unsafe if misused.

class SensorSystem {
    unowned let controller: MotorController  // unowned reference

    init(controller: MotorController) {
        self.controller = controller
    }
}

class MotorController {
    var sensorSystem: SensorSystem?

    func setupSensors() {
        sensorSystem = SensorSystem(controller: self)
    }

    deinit {
        print("MotorController deallocated")
    }
}

func testUnowned() {
    let controller = MotorController()
    controller.setupSensors()
    // sensorSystem deallocates before controller ends
}

testUnowned()
// Output: MotorController deallocated

ARC Overhead in Embedded Systems

While ARC provides safety benefits, it does introduce some overhead compared to manual memory management:

Memory Overhead:

ARC-managed class instances in Swift typically include an additional 4 or 8 bytes to store reference count metadata, depending on the system architecture, 4 bytes on 32-bit systems and 8 bytes on 64-bit systems. This metadata allows the runtime to track how many active references exist to a given object and deallocate it when no references remain. When developers use weak or unowned references, the memory footprint increases further. These references require additional data structures, such as side tables or tracking mechanisms, to manage object liveness and cleanup. In the case of weak references specifically, Swift maintains zeroing weak reference tables that automatically null out pointers once the referenced object is deallocated, ensuring memory safety.

CPU Overhead:

ARC introduces some runtime overhead due to retain and release operations, which are inserted automatically during reference assignments. These operations involve incrementing or decrementing the reference count and are especially common in code that passes objects between functions or stores them in collections. To ensure thread safety, these updates are typically implemented using atomic operations, which add further instruction cycles. In complex object graphs, ARC may also engage in cycle detection and cleanup through the use of weak references to prevent memory leaks caused by strong reference cycles. While Swift's ARC provides deterministic and efficient memory management, it does so with both memory and CPU costs that developers should consider carefully, especially in performance-critical embedded systems.

Type Safety and Error Prevention

Swift's type system prevents many common errors that plague C/C++ programs:

• Buffer Overflows: Swift arrays are bounds-checked, preventing buffer overflow vulnerabilities that are common in C.

• Null Pointer Dereferences: Swift's optional types make null pointer dereferences impossible at compile time.

• Use After Free: Swift's ownership model prevents use-after-free errors that can cause crashes or security vulnerabilities.

Now that we’ve covered Swift's memory model and ARC behavior, let’s explore how it compares to C in terms of memory usage and instruction cycles, a crucial aspect when evaluating Embedded Swift for real-world deployment.

Memory and Instruction Cycle Comparison

Understanding the performance characteristics of Swift versus C is essential for embedded systems, where every instruction cycle and byte of memory matters. While Swift brings advantages like safety and expressiveness, these benefits come with certain trade-offs in terms of memory usage and runtime behavior that embedded developers must evaluate carefully.

Memory Management:

Swift uses Automatic Reference Counting (ARC) to manage memory. ARC tracks the number of references to each object and deallocates it when no references remain. This eliminates the need for explicit free() calls but introduces overhead.

C, in contrast, uses manual memory management. Developers allocate memory using malloc and release it using free, or rely on the stack for most short-lived data.

The table below provides the memory management comparison between Swift and C:

Swift ensures safety through deterministic cleanup and predictable memory usage. But this comes at the cost of added memory and CPU overhead.

C’s approach offers complete control over memory layout and minimal runtime cost, but increases the risk of memory leaks and fragmentation without disciplined practices.

Instruction Cycle Analysis

The safety features in Swift, such as bounds checking, optional unwrapping, and ARC updates, translate into additional CPU instructions. While this can impact performance, the Swift compiler is aggressive about optimization in release builds. For example, inlining and ARC elision can remove much of the overhead in performance-critical paths.

C has no built-in safety checks, allowing it to generate highly efficient, predictable code. Developers can even use inline assembly for tight control over performance.

The table below provides the instruction cycle comparison between Swift and C:

Although Swift inserts extra instructions for safety, much of this cost can be mitigated through compiler optimization.

C has no such features by default, making it ideal for applications where performance must be tightly controlled and the developer is willing to take full responsibility for safety.

Instruction Count Comparison: Swift vs C Loop Performance

When evaluating Swift and C for embedded use, it's helpful to analyze instruction-level performance on basic operations, such as a loop that processes an array of floating-point numbers. This gives us a concrete sense of the computational cost of each language's safety and abstraction features.

Let’s consider a simple example: summing an array of Float values and returning the average. In Swift, the code uses a high-level for-in loop over an array:

Simple loop performance:

// Swift loop with safety checks
func processData(_ data: [Float]) -> Float {
    var sum: Float = 0.0
    for value in data {  // Iterator with bounds checking
        sum += value     // Safe arithmetic
    }
    return sum / Float(data.count)  // Safe division
}
// Estimated: ~8-10 instructions per iteration

Although elegant and safe, this loop includes several safety mechanisms:

1. Bounds checking on every array access

2. Reference counting if data is passed as a reference type

3. Overflow protection in debug mode

4. Optional handling or runtime checks if data might be empty

These checks introduce runtime overhead, resulting in an estimated 8–10 instructions per iteration on most platforms (depending on optimization level and target architecture). In release builds, Swift aggressively inlines and strips redundant checks, but some level of abstraction cost remains, especially compared to raw memory access in C.

Now, compare that to its equivalent in C:

// C loop without safety checks
float process_data(float* data, int count) {
    float sum = 0.0f;
    for (int i = 0; i < count; i++) {  // Direct pointer arithmetic
        sum += data[i];                // Direct memory access
    }
    return sum / count;  // Direct division (no safety check)
}
// Estimated: ~4-5 instructions per iteration

This version performs direct memory access with pointer arithmetic, no bounds checks, and no type safety. The C code is lower-level, with fewer runtime checks, and compiles down to just 4–5 instructions per iteration, depending on the target CPU and compiler flags. It is lean and fast, ideal for cycles-per-instruction-critical scenarios.

The table below shows the comparison of single loop performance between Swift and C:

Now that we’ve compared Swift and C in terms of memory and cycle costs, let’s move into the practical side: how to set up Embedded Swift on an STM32 platform and get started with real-world development.

How to Setup Embedded Swift

In this section, we'll walk through how to configure and use Embedded Swift for development on STM32 microcontrollers. STM32 is a popular family of ARM Cortex-M–based microcontrollers, commonly used in industrial, consumer, and IoT applications.

Prerequisites

Required Software:

• Swift Development Snapshot (includes the Embedded Swift toolchain)

• Swiftly - Easiest way to manage and install swift toolchains

• Swiftc - Swift Compiler command-line tool

• Python3 - Required to run scripts to convert Mach-O to binary files

• Git (to clone sample repositories) like https://github.com/swiftlang/swift-embedded-examples

• A Unix-like development environment (macOS is currently best supported)

Target Hardware: This guide focuses on STM32 microcontrollers, which are widely used in embedded applications and have excellent community support.

This guide walks you through the full setup process, from installing the required Swift toolchain to flashing the final binary onto your board. We’ll begin by installing the Swift Development Snapshot using Swiftly, a simple command-line utility for managing Swift toolchains. From there, we’ll configure the build system, set up the correct board variant, customize the build script, and compile the Swift and C source code into a binary. Finally, we’ll flash the firmware onto the STM32 using standard tools

Install Swift Development Snapshot

The easiest way to install and manage Embedded Swift toolchains is by using the swiftly tool, which simplifies downloading and using Swift snapshots.

macOS Installation:

The below steps will help install the Swift embedded toolchain:

# Using Swiftly (Recommended)
curl -O https://download.swift.org/swiftly/darwin/swiftly.pkg
installer -pkg swiftly.pkg -target CurrentUserHomeDirectory
~/.swiftly/bin/swiftly init --quiet-shell-followup
source "${SWIFTLY_HOME_DIR:-$HOME/.swiftly}/env.sh"

# Install and use development snapshot
swiftly install main-snapshot
swiftly use main-snapshot

# Verify installation
swift --version

You can clone this Github example repository:

git clone https://github.com/swiftlang/swift-embedded-examples.git 
cd swift-embedded-examples/projects/stm32-blink

The stm32-blink contains:

• Swift code that toggles GPIOs

• A C startup file with vector table

• A build.sh script that uses swiftc, clang, and a custom linker setup

Setup the STM32 Board

Tell the build script which STM32 board is being used:

export STM_BOARD=STM32F746G_DISCOVERY

You can add your own board variant by defining the appropriate memory map and compiler flags in the script.

Modify build.sh (Optional)

Ensure the script correctly locates the following:

• swiftc: should point to the toolchain you installed with Swiftly

• clang: can be macOS’s default Clang

• libBuiltin.a, crt0.s, and macho2bin.py: used to provide minimal runtime support and convert output to flashable binaries

If needed, update these paths:

SWIFT_EXEC=${SWIFT_EXEC:-$(swiftly which swiftc)}
CLANG_EXEC=${CLANG_EXEC:-$(xcrun -f clang)}
PYTHON_EXEC=${PYTHON_EXEC:-$(which python3)}

Ensure the linker flags match your target’s flash and RAM sizes.

Build and Flash the Project:

Run:

./build.sh

This compiles Swift and C code, links them, and produces a blink.bin file.

If successful, you’ll see:

.build/blink.bin  # ready to flash Step 6: Flash the Firmware to STM32

Use ST-Link tools or openocd to flash your board. Example using st-flash:

brew install stlink
st-flash write .build/blink.bin 0x8000000

You should now see an LED blinking.

Here’s a more detailed step by step approach to writing a bare metal code on STM32. For comprehensive installation guides covering other platforms (Raspberry Pi Pico, ESP32, nRF52), detailed IDE configuration, troubleshooting, and advanced examples, you can check out the official documentation:

• Complete Setup Guide: Install Embedded Swift

• Platform Examples: Swift Embedded Examples Repository

• Getting Started Tutorial: Embedded Swift on Microcontrollers

Now that we’ve set up Embedded Swift and explored how to build and run an example project, let’s look at a critical real-world scenario: interfacing Swift with low-level C drivers.

C-Swift Linkages

In many embedded projects, low-level hardware drivers are written in C because of its close-to-metal control and widespread ecosystem support. Embedded Swift supports seamless interoperability with C, which lets you reuse existing C libraries and drivers, write hardware control logic in C, and implement higher-level application logic in Swift.

This hybrid model lets you combine Swift’s safety and productivity with C’s hardware-level control, with no runtime overhead or object translation.

Let’s walk through an example where a low-level sensor driver is implemented in C and the application logic is written in Swift.

C Header File (sensor_driver.h):

This C header file defines the public interface for a low-level sensor driver. It includes standard fixed-width integer types and declares four functions:

• sensor_init(): Initializes the hardware sensor

• sensor_read_temperature() and sensor_read_humidity(): Read raw sensor values

• sensor_delay_ms(): Delays execution for a given number of milliseconds

This interface acts as a bridge between Swift and C. Swift will link to these functions by name, no wrappers or bindings required.

#ifndef SENSOR_DRIVER_H
#define SENSOR_DRIVER_H

#include <stdint.h>

// Low-level sensor driver functions
void sensor_init(void);
uint32_t sensor_read_temperature(void);
uint32_t sensor_read_humidity(void);
void sensor_delay_ms(uint32_t milliseconds);

#endif

C Implementation (sensor_driver.c):

This implementation assumes the sensor is memory-mapped at a fixed address (0x40001000). Each register, temperature, humidity, and control, is accessed by offset from that base address.

The sensor_init() function writes 0x01 to the control register, presumably enabling or starting the sensor hardware.

The sensor_read_temperature() method and sensor_read_humidity() method reads from memory-mapped registers and return the raw ADC values from the sensor.

The sensor_delay_ms() method performs a simple busy-wait loop using nop (no-operation) instructions to approximate a delay. This is suitable for short, coarse-grained delays in bare-metal contexts.

#include "sensor_driver.h"

// Hardware register addresses
#define SENSOR_BASE_ADDR    0x40001000
#define TEMP_REG_OFFSET     0x00
#define HUMIDITY_REG_OFFSET 0x04
#define CONTROL_REG_OFFSET  0x08

void sensor_init(void) {
    // Initialize sensor hardware
    volatile uint32_t* control_reg = (volatile uint32_t*)(SENSOR_BASE_ADDR + CONTROL_REG_OFFSET);
    *control_reg = 0x01; // Enable sensor
}

uint32_t sensor_read_temperature(void) {
    volatile uint32_t* temp_reg = (volatile uint32_t*)(SENSOR_BASE_ADDR + TEMP_REG_OFFSET);
    return *temp_reg;
}

uint32_t sensor_read_humidity(void) {
    volatile uint32_t* humidity_reg = (volatile uint32_t*)(SENSOR_BASE_ADDR + HUMIDITY_REG_OFFSET);
    return *humidity_reg;
}

void sensor_delay_ms(uint32_t milliseconds) {
    // Simple delay implementation
    for (uint32_t i = 0; i < milliseconds * 1000; i++) {
        __asm__("nop");
    }
}

Swift Code Using C Driver:

To use these C functions from Swift, you declare them using @_silgen_name, which tells the Swift compiler to link directly to these symbol names at runtime.

The SensorController class encapsulates sensor-related logic. In its init() method, it calls the sensor_init() function defined in C to initialize the sensor hardware.

The readSensors() method reads the raw values from the C driver, converts them into human-readable units using helper functions, stores them internally, and returns the processed values.

The convertTemperature() and convertHumidity() conversion methods apply a basic linear formula to turn raw ADC values into temperature in Celsius and humidity in percentage, respectively. These formulas would be based on the specific sensor’s datasheet.

The checkThresholds() method applies simple threshold logic, a good example of where Swift’s readability and type safety shine. You could easily expand this logic to include error bounds, state machines, or alerts.

// Import C driver functions

/*
These declarations match the C function signatures exactly. 
They allow Swift to invoke the C functions as if they were native Swift functions 
— with zero overhead.
*/
@_silgen_name("sensor_init")
func sensor_init()

@_silgen_name("sensor_read_temperature")
func sensor_read_temperature() -> UInt32

@_silgen_name("sensor_read_humidity")
func sensor_read_humidity() -> UInt32

@_silgen_name("sensor_delay_ms")
func sensor_delay_ms(_ ms: UInt32)

// Swift sensor controller using C driver
class SensorController {
    private var lastTemperature: Float = 0.0
    private var lastHumidity: Float = 0.0

    init() {
        // Initialize the C driver
        sensor_init()
    }

    func readSensors() -> (temperature: Float, humidity: Float) {
        // Read raw values from C driver
        let rawTemp = sensor_read_temperature()
        let rawHumidity = sensor_read_humidity()

        // Convert raw values to meaningful units in Swift
        let temperature = convertTemperature(rawValue: rawTemp)
        let humidity = convertHumidity(rawValue: rawHumidity)

        // Store for comparison
        lastTemperature = temperature
        lastHumidity = humidity

        return (temperature: temperature, humidity: humidity)
    }

    private func convertTemperature(rawValue: UInt32) -> Float {
        // Convert raw ADC value to Celsius
        return (Float(rawValue) * 3.3 / 4095.0 - 0.5) * 100.0
    }

    private func convertHumidity(rawValue: UInt32) -> Float {
        // Convert raw ADC value to percentage
        return Float(rawValue) * 100.0 / 4095.0
    }

    func checkThresholds() -> Bool {
        // Swift logic for threshold checking
        let tempThreshold: Float = 25.0
        let humidityThreshold: Float = 60.0

        return lastTemperature > tempThreshold || lastHumidity > humidityThreshold
    }
}

// Main application loop
func main() -> Never {
    let sensorController = SensorController()

    while true {
        // Read sensors using Swift controller with C driver
        let readings = sensorController.readSensors()

        // Process data with Swift's type safety and expressiveness
        if sensorController.checkThresholds() {
            print("Warning: Temperature: \(readings.temperature)°C, Humidity: \(readings.humidity)%")
        } else {
            print("Normal: Temperature: \(readings.temperature)°C, Humidity: \(readings.humidity)%")
        }

        // Delay using C driver function
        sensor_delay_ms(1000) // 1 second delay
    }
}

The func main() is the main event loop standard for embedded systems. It creates the sensor controller, reads sensor data in a loop, checks thresholds, and prints results accordingly. The loop includes a delay (via the C driver) to avoid hammering the sensor continuously.

In an actual embedded context, instead of using print(), you might blink an LED, send UART messages, or log data to memory.

With Embedded Swift and C now working together, let’s explore what lies ahead. The next section outlines ongoing improvements, emerging use cases, and research directions that are shaping the future of Embedded Swift.

Future Work

Embedded Swift is still a young but rapidly evolving technology. Its modern language features, type safety, and performance make it an attractive option for embedded development, and ongoing work is expanding its capabilities, reach, and ecosystem.

Ongoing Improvements

Compiler Optimizations: The Swift compiler team is actively improving code generation for embedded targets, including:

• Reducing binary size

• Minimizing ARC overhead

• Improving static dispatch performance

Hardware Support: Embedded Swift can target a wide variety of ARM and RISC-V microcontrollers, which are popular for building industrial applications. Support for additional architectures is being developed.

Tooling Enhancements: Tooling support for Embedded Swift is still evolving, but several community-driven and open-source efforts are making development more accessible:

• Build Systems: The Swift Embedded Working Group provides example projects that adapt Swift Package Manager (SwiftPM) for cross-compilation. Custom linker scripts and build helpers are available for platforms like STM32 and nRF52.

• Debugging Support: Developers can debug Embedded Swift programs using existing tools like GDB or OpenOCD, provided the build includes appropriate debug symbols. While not yet officially streamlined, this approach enables step-through debugging on real hardware.

• IDE Integration: There is no official IDE support yet, but some developers use VSCode with Swift syntax highlighting and external build tasks. These setups are still manual but serve as early prototypes for embedded workflows.

Emerging Use Cases

There are a number of emerging use cases for embedded Swift. For example, Swift’s memory safety, type guarantees, and protocol-oriented design make it ideal for secure and scalable IoT devices, especially where firmware bugs could affect user safety or privacy.

The automotive sector is also exploring Swift for infotainment systems, driver assistance features, and safety-critical logic (where deterministic execution and safety matter).

Swift’s expressive syntax and compile-time safety make it suitable for industrial automation – think real-time control loops, sensor fusion systems, and edge devices in smart manufacturing.

It’s also useful for medical devices, as it aligns well with strict medical regulations around memory safety, type guarantees, and predictable resource usage.

Community and Ecosystem

Open Source Projects

The Swift Embedded working group maintains example repositories showcasing how to use Embedded Swift on microcontrollers such as STM32, nRF52, and ESP32. Early-stage libraries for UART, GPIO, and basic peripherals are emerging, though the ecosystem is still young compared to C or Rust.

Learning Resources

While Embedded Swift is not yet widely taught in formal curricula, community tutorials and exploratory projects (for example, Swift for Arduino) are lowering the barrier for hobbyists and independent learners. As tooling matures, educational adoption is likely to follow.

Industry Interest

Embedded Swift is beginning to draw attention from developers and companies looking for safer, more maintainable alternatives to C. Although large-scale adoption remains limited, use cases like rapid prototyping, IoT development, and internal experimentation are gaining traction.

Conclusion

Embedded Swift represents a major step forward in embedded programming. By combining the power and safety of Swift with the low-level control needed for microcontrollers, it offers an exciting alternative to traditional C and C++ development.

While C will remain essential for hardware-level programming and performance-critical paths, Swift brings compelling advantages to many embedded scenarios:

• Memory safety: Swift eliminates entire categories of bugs such as buffer overflows, use-after-free, and null pointer dereferencing.

• Type safety: Many logic errors are caught at compile time, long before they can cause runtime failures.

• Modern language features: Developers can use functional paradigms, generics, and protocol-oriented design even in embedded code.

• C interoperability: Swift works seamlessly with existing C libraries, allowing gradual adoption without rewriting low-level drivers.

• Developer productivity: Clear syntax, automatic memory management, and strong tooling lead to faster development and easier maintenance.

Government and regulatory bodies are increasingly encouraging or mandating the use of memory-safe programming languages to reduce vulnerabilities in critical software systems. For example:

• In 2022, the U.S. National Security Agency (NSA) recommended moving away from unsafe languages like C/C++ for new software projects, promoting memory-safe alternatives.

• In June 2025, the NSA and CISA released a joint Cybersecurity Information Sheet titled “Memory Safe Languages: Reducing Vulnerabilities in Modern Software Development”, which emphasized that memory safety flaws remain a persistent risk, and organizations should develop strategies to adopt memory-safe programming languages in new systems.

• The U.S. Cybersecurity and Infrastructure Security Agency (CISA) and NIST have echoed similar guidance in the context of national cybersecurity.

While these documents do not mention Swift explicitly, Swift's strong type system, ARC-based memory model, and compile-time safety guarantees align closely with the goals outlined in these recommendations. As such, it offers a practical, developer-friendly path toward safer embedded development.

Swift may not be the right fit for every embedded system. In applications where every byte of memory or instruction cycle is critical, real-time guarantees are hard requirements, or toolchain maturity is essential (for example, RTOS integration, static analyzers), C or Rust may still be preferred.

But in many modern embedded applications, especially those involving rapid prototyping, fast product iteration, safety-critical or maintainable firmware, and interoperability with existing C codebases, Swift offers a highly productive and safe development experience.

Embedded Swift is still maturing, but its momentum is undeniable. With ongoing compiler work, community-driven examples, and growing interest from developers, it’s poised to play a major role in the future of embedded systems.

Whether you're building an IoT device, a piece of industrial equipment, or a proof-of-concept wearable, Swift can help you write safer, more expressive firmware, without giving up performance or control.

Swift can be especially powerful during the prototyping phase, when the primary goal is to validate functionality quickly and safely. And with its increasing support for multiple hardware platforms, it offers a strong foundation for bringing modern software development practices to the embedded world.

For many app developers, including me, writing the networking layer of an application is a familiar and tedious process. You write and test your first call and after that, it involves a repetitive cycle of tasks.

This is how it would look in the case of Swift:

1. You create a URLSession Instance.

2. You create a URLRequest Object.

3. You create the @Codable models to match the expected input and output from the server.

You do the above steps for each API endpoint you have on your backend that your app uses. Not only is this process time-consuming and not challenging for developers, it’s also error prone.

In the above case, if there was a minor change in the backend API – perhaps a renamed field or a new property – this would lead to the app potentially breaking. But you wouldn’t know this until you shipped it to QA or in a worse case, your consumer. This is where the OpenAPI Specification emerges as a modern, robust solution.

In this tutorial, you’ll learn what OpenAPI is and how it can help make your development process better. After that, we’ll implement OpenAPI by creating a small SwiftUI app and using OpenAPI methodologies to interface with the JSONPlaceholder API. Let’s get started.

Who is This Guide For?

This guide is intended both for new developers looking for best practices and for experienced developers looking to implement or learn more about the OpenAPI Specification. Let’s get into it.

Table of Contents

• What is OpenAPI and Why Should You Care?

  • Benefits for Swift (iOS) Developers

• A Practical Guide to Implementing This Solution

  • Step 1: Create a good openapi.yaml file (the specification)

  • Step 2: Set up your project

  • Step 3: Write a wrapper

  • Step 4: Call the wrapper and display the data

• Potential Pitfalls

  • Verbose or ugly generated code

  • Large Specs and Performance Issues

  • Unsupported Spec Features

• Conclusion: Embrace Spec-Driven Development

What is OpenAPI and Why Should You Care?

At its core, the OpenAPI Specification provides a standard, language-agnostic interface for describing RESTful APIs. This specification, once populated, allows both humans and computers to discover and understand the capabilities of a service without needing to access the source code or the network requests.

The power of OpenAPI is that it acts as a formal contract between different parts of the system. This contract helps both frontend and backend programmers by removing ambiguity during design process. This also has added benefit of using code generators to generate boiler-plate code both on backend and on the client ( which we will also discuss today ).

Traditionally when you want to create a new API in a team, either the PM, the frontend engineer, or the backend engineer takes it upon themselves to request it. Then the backend team builds it and documents it. This in turn is used by the front end team to use the API.

Some Requester → Backend Team → Documentation → Frontend Team

If you’re using OpenAPI, when someone makes a request for a new API, it is formalized into a specification after deliberations with both the frontend and the backend team. This then serves as the source of truth and is used to generate the backend and the frontend code without as much interdependence.

Some Requester → All Teams → Specification → All Teams.

This not only streamlines the process of adding new APIs, but provides a definitive source of truth for each endpoint. This also makes it so that frontend engineers and backend engineers are not misaligned about a provided parameter in the result being an Int or a String and so on. It’s all in the Spec.

Benefits for Swift (iOS) Developers

Adopting OpenAPI and swift-openapi-generator brings a host of tangible benefits to the Swift/App development process. It transforms how applications interact with web services in a few key ways.

Reduced Development Time and Cost

The most immediate improvement you will see is the significant reduction in boilerplate code you have to write. The generator automates the creation of what is called boilerplate code or ceremonial code. This is the repetitive logic for network requests, response handling, and data model definitions.

By delegating this work, developers can work on the core features of the application which leads to faster and more interesting development cycles.

Compile Time Type Safety

This has been a major improvement for me personally. Instead of relying on the “strongly” typed keys for JSON parsing, we now work with strongly typed models. The generator creates native Swift struct and enum types directly from the schemas defined in the OpenAPI document. This brings the power of a strongly-typed system to the networking and parsing layer.

For example, if the return value of an API is made optional, instead of crashing at runtime, we will fail to compile at build time. This forces us to address this issue right away.

Improved Collaboration and Interoperability

This makes sure that all the developers are on the same page with regard to a given endpoint. And since this specification is language agnostic, it will serve as a universal language for all teams involved in the project – mobile, web and backend.

Other Tooling

Once you have a specification, you can use that to power a wide variety of tools. You can generate interactive documentation, create mock servers for frontend development, and run automated tests.

Alright hopefully you’re sold – so now how do you implement this into your project?

A Practical Guide to Implementing This Solution

We’ll now take a look at a practical example so you can understand how you can implement this in a project. This involves:

• Creating an openapi.yaml file to describe the API specification.

• Configuring and integrating swift-openapi-generator into a SwiftUI application.

• Prototyping an app that fetches and displays a list of posts from the https://jsonplaceholder.typicode.com/

To follow along, you will need Xcode installed and a basic understanding of Swift programming and SwiftUI for App development.

Step 1: Create a good openapi.yaml file (the specification)

The quality of a specification is really important because it directly determines the quality of the code produced by swift-openapi-generator. If you don’t have a good specification, you might run into several issues that developers often complain about, like confusing and long method names.

For example, it might generate something like get_all_my_meal_recipes_hyphen_detailed. This might happen because the generator is forced to create a new name based on the API path if the identifier is not provided in the spec. So, instead of dealing with these issues one after the other, we will create a good clear specification to start with.

Since we’re using the jsonplaceholder as our backend server, we are limited by what tweaks we can make – but it is a fantastic project that lets us mimic a backend server.

In general, an OpenAPI.yaml file contains:

1. OpenAPI Info and servers – This will provide the metadata about the API like the OpenAPI version, which server to point to for calls, and so on.

2. Paths – This will provide the available endpoints. In our case, it can contain /posts as one of them. We also will have to mention the kind of endpoint (get, post, put, and so on)

3. OperationID – This field instructs the generator to create a clear method with this name.

4. Responses – This defines the possible outcomes of an API call. We will specify the structure of a successful 200 OK response or any other errors here.

5. Components / Schemas – This defines all the reusable components and data models. If we have a Post schema definer here, the generator will use this to create a Post struct in Swift to match this.

Keeping in mind all these elements, I compiled a yaml file for us to use for this tutorial:

# openapi.yaml
openapi: "3.0.3"
info:
  title: "JSONPlaceholder API"
  version: "1.0.0"
servers:
  - url: "https://jsonplaceholder.typicode.com"
paths:
  /posts:
    get:
      summary: "Get all posts"
      operationId: "getPosts"
      responses:
        "200":
          description: "A list of posts"
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: "#/components/schemas/Post"
components:
  schemas:
    Post:
      type: object
      required:
        - userId
        - id
        - title
        - body
      properties:
        userId:
          type: integer
        id:
          type: integer
        title:
          type: string
        body:
          type: string

The first line here, openapi: “3.0.3”, just tells the generators and parsers that we are using version 3.0.3.

Next, we have some more metadata – the name and version of the API. We also have the server we are calling with our APIs.

After defining this metadata, we now define our endpoints. For the sake of this example, let’s assume that we only have one endpoint to call to get posts. We represent this by saying /posts under paths. We then specify which kind it is by specifying get:.

We give a short description of what it does in the summary and then specify an operationId which is what we this function will be called in our generated code. We also specify exactly what structure the response will have, that is, a JSON of an array of Posts.

We then list any components we have across our APIs like the Post. Note that we are using the Post schema in the return response structure before we define it further down. The schemas in components will determine the Model structs we will generate using this yaml file.

Step 2: Set up your project

Create a new SwiftUI project. For the purpose of this tutorial, we’ll use an iOS app – but you can do this with any app. Select Swift as the language and SwiftUI for the interface.

Add the openapi.yaml file we just created to this project. (You can also create this file in Xcode and copy, paste from the script above.)

Now, add the following swift packages to the project. (Note: Please read the entire section about adding packages before you proceed.)

1. Swift OpenAPI Generator – https://github.com/apple/swift-openapi-generator – The Core Generator Plugin.

   

   

2. Swift OpenAPI Runtime – https://github.com/apple/swift-openapi-runtime – This contains the common types and protocols used by the code generated by the generator plugin.

   

3. Swift OpenAPI URLSession – https://github.com/apple/swift-openapi-urlsession – This is a transport layer that allows the generated code to use the Apple URLSession to make network requests.

   

One major caveat to note here when adding these packages is that The Swift OpenAPI Generator should not be added to your project target. This is because we’re only using this to generate the code, but we’re not using it in the app.

If you get this error: swift-openapi-generator/Sources/_OpenAPIGeneratorCore/PlatformChecks.swift:21:5 _OpenAPIGeneratorCore is only to be used by swift-openapi-generator itself—your target should not link this library or the command line tool directly. – then you made this mistake.

The easiest way to fix this is removing the package and adding it again. Or you can go to Project → Target → Build Phases → Link Binary with Libraries → Remove Swift OpenAPI Generator.

Now that we added these generator and runtime plugins, we need to give the generator some instructions on what to generate. You can do this with an openapi-generator-config.yaml file. For our project, use the following file. It’s really simple:

generate:
  - types
  - client

This tells our generator to generate the types – the swift structs, enums, and so on from the schema section of the file, and the client – the main class which interacts with the networking logic.

Save this into an openapi-generator-config.yaml file as shown.

And finally, we want the generator to run whenever we want to build this application/target. We can specify this in the Build Phases tab of the target. Under the “ Target → Build Phases → Run Build Tool Plug-ins” , add the OpenAPIGenerator Plugin.

The first time the project is built after setting this, Xcode will display a security dialog. This will let us “Trust and Enable” for this plugin. It’s a one time confirmation that gives this plugin the permission required to run during the build process.

As soon as you build the second time after giving these permissions, you will generate the files. You might not see any changes in the Xcode window itself. But if you’re curious to see the result, go to this folder.

DerivedData → <ProjectName>*identifier → Build → intermediates.noindex → BuildToolPluginIntermediates → <TargetName>.output → <TargetName> → OpenAPIGenerator → GeneratedSources

More on derived data folder here: https://gayeugur.medium.com/derived-data-2e9468c6da9b if you’re curious.

Keep in mind that this location might vary based on Xcode version, OpenAPI version, and your project settings. But you don’t need to worry about the file location.

You will see three files called Client.swift, Types.swift, and Server.swift.

These are the files that the our generator created and populated with the types and functions we need.

In the next section, we discuss how to use these files to make calls to the server.

Step 3: Write a wrapper

While it’s certainly possible to make the calls to server using just the generated code (Client) type throughout our application, a more maintainable approach is to use a wrapper around these types. This will provide a stable, clean interface for the rest our our app to use, and it decouples feature code from the generated code.

I can hear you thinking: “Wait a second. Isn’t the entire purpose of generating this code to avoid this boilerplate abstraction?”

While it adds some abstraction on top of the generated code, it’s valuable to have this for number of reasons. Here are but a few of them:

1. Better naming. The generated Post struct right now will be called Components.Schemas.Post.

2. If you ever want to move away from the generator, an abstraction is really helpful.

3. If you want to Mock this server call, you can do this via the abstraction.

4. UI Optimization. You might want to flatten the structure of a model to reduce the number of computed variables in there, and so on.

So, we want to wrap this around a file called WebService.swift:

// WebService.swift
import Foundation
import OpenAPIURLSession

// A clean, app-specific Post model.
// This decouples views from the generated types.
struct AppPost: Identifiable, Codable {
    let id: Int
    let title: String
    let body: String
}

class WebService {
    private let client: Client

    init() {
        // The server URL and transport are from the generated code.
        // `Servers.Server1.url()` corresponds to the first URL in the `servers` array of the spec.
        self.client = Client(
            serverURL: try! Servers.Server1.url(),
            transport: URLSessionTransport()
        )
    }

    func getPosts() async throws -> [AppPost] {
        // Call the generated method, which was named using `operationId`.
        let response = try await client.getPosts(.init())

        // The generated response is a type-safe enum covering all documented status codes.
        switch response {
        case.ok(let okResponse):
            // The body is also a type-safe enum for different content types.
            switch okResponse.body {
            case.json(let posts):
                // Map the generated `Components.Schemas.Post` to our clean `AppPost` model.
                return posts.map { post in
                    AppPost(id: post.id, title: post.title, body: post.body)
                }
            }
        // The generator forces the handling of other documented responses.
        // Our simple spec only has a 200, so any other response is undocumented.
        case.undocumented(statusCode: let statusCode, _):
            throw URLError(.badServerResponse, userInfo: ["statusCode": statusCode])
        }
    }
}

Let’s go through this file to understand what we’re doing.

First, we import OpenAPIUrlSession along with Foundation. This allows us to call the server, get a response and parse that response.

Next, we define the new AppPost struct. This is meant to be the representation of a Post in the App. In the generated Types.Swift file, we have the generated Post structure. This is defined as:

/// - Remark: Generated from `#/components/schemas/Post`.
        internal struct Post: Codable, Hashable, Sendable {
            /// - Remark: Generated from `#/components/schemas/Post/userId`.
            internal var userId: Swift.Int
            /// - Remark: Generated from `#/components/schemas/Post/id`.
            internal var id: Swift.Int
            /// - Remark: Generated from `#/components/schemas/Post/title`.
            internal var title: Swift.String
            /// - Remark: Generated from `#/components/schemas/Post/body`.
            internal var body: Swift.String
            /// Creates a new `Post`.
            ///
            /// - Parameters:
            ///   - userId:
            ///   - id:
            ///   - title:
            ///   - body:
            internal init(
                userId: Swift.Int,
                id: Swift.Int,
                title: Swift.String,
                body: Swift.String
            ) {
                self.userId = userId
                self.id = id
                self.title = title
                self.body = body
            }
            internal enum CodingKeys: String, CodingKey {
                case userId
                case id
                case title
                case body
            }
        }

As you can see, our AppPost struct is different from this generated type. We omit the userId since we do not care about it (at least for now).

Back to the WebService class, we see a client attribute. This is a generated type variable that will let us interact with the servers. In the initializer of the WebService class, we create a new Client using the first server URL we specified in the schema and use the URLSessionTransport object for making these calls.

We then define our methods. In this case, our getPosts() function which returns [AppPost] array.

let response = try await client.getPosts(.init()) will call the function getPosts() on the Client object. The Client.getPosts() function here takes in an input struct called Operations.getPosts.Input which is initialized by the .init() passed here.

This generated response is a type-safe enum covering all documented codes. (Currently only 200 in our yaml file). So, we use a simple switch to look at both these cases and further use more switch statements to get the proper response. You can see how much easier this is than to parse the response manually.

Once we get the Components.Schemas.Post response, we map and convert it into [AppPost] array and return it.

Now, let’s use this wrapper to display data in our app.

Step 4: Call the wrapper and display the data

We’re at the final step now. We’ll use the wrapper we created to display the fetched posts. We’ll also use a state variable to store our AppPost array in our ContentView view. We’ll then call getPosts() when the view is first displayed to the user.

// ContentView.swift
import SwiftUI

struct ContentView: View {
    @State private var posts: [AppPost] = []
    @State private var errorMessage: String?

    private let webService = WebService()

    var body: some View {
        NavigationStack {
            List(posts) { post in
                VStack(alignment:.leading, spacing: 8) {
                    Text(post.title)
                       .font(.headline)
                    Text(post.body)
                       .font(.subheadline)
                       .foregroundColor(.secondary)
                }
               .padding(.vertical, 4)
            }
           .navigationTitle("Posts")
           .task {
                await loadPosts()
            }
           .overlay {
                if let errorMessage {
                    ContentUnavailableView("Error", systemImage: "xmark.octagon", description: Text(errorMessage))
                } else if posts.isEmpty {
                    ProgressView()
                }
            }
        }
    }

    func loadPosts() async {
        self.errorMessage = nil
        do {
            self.posts = try await webService.getPosts()
        } catch {
            self.errorMessage = error.localizedDescription
        }
    }
}

#Preview {
    ContentView()
}

You can see the dummy posts in the Preview. As you can see, all we had to do was call the webService.getPosts() to populate the variable.

You might be thinking that this is a lot of setup for a simple struct like Post for which we had to create a wrapper called AppPost anyway. But if you had ten types like this and twenty endpoints to call? You wouldn’t have to deal with a lot of repetitive, error-prone code.

Potential Pitfalls

Unfortunately, no process is perfect. You might still face a lot of issues with generated code and this method. I’ve listed some of them here and how to deal with them.

Verbose or ugly generated code

If you have very verbose or ugly generated code, the problem is almost always the missing operationId for an API path. If you don’t specify one, the generator must create a name from the path and the HTTP method with results in long unwieldy names. Adding a clear operationId will mitigate this issue.

Large Specs and Performance Issues

If you have a very large Spec file, generating a client for this entire specification can significantly increase the compile time. It can also result in absolutely massive Types.swift and Client.swift files.

There is a filter option in the openapi-generator-config.yaml file that will allow the generator to include only parts of the spec that are relevant to the application to improve build times and so on. But if you want everything in an API that has hundreds of endpoints, the only way to reduce compile times is to avoid regenerating this every time and decouple this step from the regular build process.

Unsupported Spec Features

While the swift package, swift-openapi-generator, is robust, it does not support all the features included in the specification. I had issues with some features of the newer spec version ( 3.1.1 and had to downgrade to 3.0.3 to make it work well ).

There are also known issues like lack of support for certain types of recursive schemas. Sometimes, the generator errors out and fails and some other times, it generates incomplete types – which can result in a few hours of debugging (I speak from experience).

In any case, knowing the limits of this generator can be helpful in avoiding issues it might cause. Also keep in mind that it is always getting better thanks to its open source nature.

Conclusion: Embrace Spec-Driven Development

In this guide, you navigated the journey of adopting swift-openapi-generator – from understanding the power of API contracts to building a functional SwiftUI app. You also learned about the real life challenges of this process. While there is an initial learning curve, the benefits of this approach are profound.

The core tenet of this approach is to foster more disciplined and more robust method for building applications. By making the OpenAPI document the single source of truth, you make sure that both the frontend and backend are perfectly in sync in perpetuity.

Using this approach also results in more type-safe, maintainable code. The result is less time spent on writing boilerplate and debugging random integration errors and more time spent creating the app itself.

For developers ready to explore further, please checkout the official swift-openapi-generator repository on Github here: https://github.com/apple/swift-openapi-generator.

You can follow me on GitHub and Hashnode for my other posts and projects.

We just released a full course on the freeCodeCamp.org YouTube channel that will teach you the Swift programming language.

Vandad Nahavandipoor teaches this course. He currently works as a lead iOS developer and he has created many other popular courses.

In this course you will learn every modern aspect of Swift as a programming language including, variables, constants, functions, structures, classes, protocols. extensions, asynchronous programming, generics and much more. This course will lay the foundation for learning Swift for those who are not familiar with Swift already.

Here are the sections in this course:

• Variables
• Operators
• If and else
• Functions
• Closures
• Structures
• Enumerations
• Classes
• Protocols
• Extensions
• Generics
• Optionals
• Error Handling
• Collections
• Equality and Hashing
• Custom Operators
• Asynchronous Programming

Watch the full course on the freeCodeCamp.org YouTube channel (7-hour watch).

The Swift programming language was created by Apple in 2014. It's the official language that works with the whole Apple Operating Systems lineup: iOS, iPadOS, watchOS, macOS, and tvOS.

Swift is an open source, general purpose, compiled programming language that's statically typed.

Every value has a type assigned. The type of a value is always checked when used as an argument or returned, at compile time. If there is a mismatch, the program will not compile.

Swift's compiler is LLVM, and it is included within Xcode, the standard IDE you use for Apple software development.

Swift is a modern programming language that was designed to "fit" in an ecosystem that was previously designed for a different programming language called Objective-C.

Most of the software running on the iPhone and Mac today is based on Objective-C code, even for official Apple apps. But Swift usage is gaining traction year after year. While Objective-C will be used for years to maintain and improve existing apps, new applications are likely going to be created with Swift.

Before Apple introduced Swift, Objective-C was heavily developed to introduce new capabilities and features. But in the recent years this effort has decreased a lot in favor of Swift development.

This does not mean Objective-C is dead or not worth learning: Objective-C is still an essential tool for any Apple developer.

That said, I am not going to cover Objective-C here, because we're focusing on Swift – the present and future of the Apple platform.

In just 6 years, Swift has gone through 5 major versions, and we're now (at the time of writing) at version 5.

Swift is famously Apple's products language, but it is not an Apple-only language. You can use it on several other platforms.

It is open source, so porting the language to other platforms does not require any permission or licensing, and you can find Swift projects to create Web servers and APIs (https://github.com/vapor/vapor) as well as projects to interact with microcontrollers.

Swift is a general-purpose language, built with modern concepts, and it has a bright future.

What We'll Cover Here

The goal of this book is to get you up and running with Swift, starting from zero.

If you have a Mac or an iPad, I recommend you to download the Playgrounds application made by Apple from the App Store.

This app lets you run snippets of Swift code without having to create a full app first. It's a very handy way to test your code, not just when you start learning, but whenever you need to try some code.

It also contains a series of awesome examples and tutorials to expand your Swift and iOS knowledge.

Note: You can get a PDF and ePub version of this Swift Beginner's Handbook

• Introduction to Swift
• Variables in Swift
• Objects in Swift
• Operators in Swift
• Conditionals in Swift
• Loops in Swift
• How to Write Comments in Swift
• Semicolons in Swift
• Numbers in Swift
• Strings in Swift
• Booleans in Swift
• Arrays in Swift
• Sets in Swift
• Dictionaries in Swift
• Tuples in Swift
• Optionals and nil in Swift
• Enumerations in Swift
• Structures in Swift
• Classes in Swift
• Functions in Swift
• Protocols in Swift
• Where to Go From Here

Variables in Swift

Variables let us assign a value to a label. We define them using the var keyword:

var name = "Roger"
var age = 8

Once a variable is defined, we can change its value:

age = 9

Variables that you do not want to change can be defined as constants, using the let keyword:

let name = "Roger"
let age = 8

Changing the value of a constant is forbidden.

You can't change the value of a constant or you'll get this error

When you define a variable and you assign it a value, Swift implicitly infers the type of it.

8 is an Int value.

"Roger" is a String value.

A decimal number like 3.14 is a Double value.

You can also specify the type at initialization time:

let age: Int = 8

But it's typical to let Swift infer it, and it's mostly done when you declare a variable without initializing it.

You can declare a constant, and initialize it later:

let age : Int

age = 8

Once a variable is defined, it is bound to that type. You cannot assign to it a different type, unless you explicitly convert it.

You can't do this:

var age = 8
age = "nine"

Cannot assign value of type 'String' to type 'Int' error

Int and String are just two of the built-in data types provided by Swift.

Objects in Swift

In Swift, everything is an object. Even the 8 value we assigned to the age variable is an object.

In some languages, objects are a special type. But in Swift, everything is an object and this leads to one particular feature: every value can receive messages.

Each type can have multiple functions associated to it, which we call methods.

For example, talking about the 8 number value, we can call its isMultiple method, to check if the number is a multiple of another number:

isMultiple method

A String value has another set of methods.

A type also has instance variables. For example the String type has the instance variable count, which gives you the number of characters in a string:

instance variable count

Swift has 3 different object types, which we'll see more in details later on: classes, structs and enums.

Those are very different, but they have one thing in common: to object type, we can add methods, and to any value, of any object type, we can send messages.

Operators in Swift

We can use a wide set of operators to operate on values.

We can divide operators in many categories. The first is the number of targets: 1 for unary operators, 2 for binary operators or 3 for the one and only ternary operator.

Then we can divide operators based on the kind of operation they perform:

• assignment operator
• arithmetic operators
• compound assignment operators
• comparison operators
• range operators
• logical operators

plus some more advanced ones, including nil-coalescing, ternary conditional, overflow, bitwise and pointwise operators.

Note: Swift allows you to create your own operators and define how operators work on your types you define.

Assignment operator in Swift

You use the assignment operator to assign a value to a variable:

var age = 8

Or to assign a variable value to another variable:

var age = 8
var another = age

Arithmetic operators in Swift

Swift has a number of binary arithmetic operators: +, -, *, / (division), % (remainder):

1 + 1 //2
2 - 1 //1
2 * 2 //4
4 / 2 //2
4 % 3 //1
4 % 2 //0

- also works as a unary minus operator:

let hotTemperature = 20
let freezingTemperature = -20

You can also use + to concatenate String values:

"Roger" + " is a good dog"

Compound assignment operators in Swift

The compound assignment operators combine the assignment operator with arithmetic operators:

• +=
• -=
• *=
• /=
• %=

Example:

var age = 8
age += 1

Comparison operators in Swift

Swift defines a few comparison operators:

• ==
• !=
• >
• <
• >=
• <=

You can use those operators to get a boolean value (true or false) depending on the result:

let a = 1
let b = 2

a == b //false
a != b //true
a > b // false
a <= b //true

Range operators in Swift

Range operators are used in loops. They allow us to define a range:

0...3 //4 times
0..<3 //3 times

0...count //"count" times
0..<count //"count-1" times

Here's a sample usage:

let count = 3
for i in 0...count {
  //loop body
}

Logical operators in Swift

Swift gives us the following logical operators:

• !, the unary operator NOT
• &&, the binary operator AND
• ||, the binary operator OR

Sample usage:

let condition1 = true
let condition2 = false

!condition1 //false

condition1 && condition2 //false
condition1 || condition2 //true

Those are mostly used in the if conditional expression evaluation:

if condition1 && condition2 {
  //if body
}

Conditionals in Swift

if statements in Swift

if statements are the most popular way to perform a conditional check. We use the if keyword followed by a boolean expression, followed by a block containing code that is run if the condition is true:

let condition = true
if condition == true {
    // code executed if the condition is true
}

An else block is executed if the condition is false:

let condition = true
if condition == true {
    // code executed if the condition is true
} else {
    // code executed if the condition is false
}

You can optionally wrap the condition validation into parentheses if you prefer:

if (condition == true) {
    // ...
}

And you can also just write:

if condition {
    // runs if `condition` is `true`
}

or

if !condition {
    // runs if `condition` is `false`
}

One thing that separates Swift from many other languages is that it prevents bugs caused by erroneously doing an assignment instead of a comparison. This means you can't do this:

if condition = true {
    // The program does not compile
}

The reason is that the assignment operator does not return anything, but the if conditional must be a boolean expression.

switch statements in Swift

Switch statements are a handy way to create a conditional with multiple options:

var name = "Roger"

switch name {
case "Roger":
    print("Hello, mr. Roger!")
default: 
    print("Hello, \(name)")
}

When the code of a case ends, the switch exits automatically.

A switch in Swift needs to cover all cases. If the tag, name in this case, is a string that can have any value, we need to add a default case, mandatory.

Otherwise with an enumeration, you can simply list all the options:

enum Animal {
    case dog
    case cat
}

var animal: Animal = .dog

switch animal {
case .dog:
    print("Hello, dog!")
case .cat:
    print("Hello, cat!")
}

A case can be a Range:

var age = 20

switch age {
case 0..<18:
    print("You can't drive!!")
default: 
    print("You can drive")
}

Ternary conditional operator in Swift

The ternary conditional operator is a shorter version of an if expression. It allows us to execute an expression if a condition is true, and another expression if the condition is false.

Here is the syntax:

`condition` ? `value if true` : `value if false`

Example:

let num1 = 1
let num2 = 2

let smallerNumber = num1 < num2 ? num1 : num2 

// smallerNumber == 1

The syntax is shorter than an if statement, and sometimes it might make more sense to use it.

Loops in Swift

for-in loops in Swift

You can use for-in loops to iterate a specific amount of times, using a range operator:

for index in 0...3 {
  //iterate 4 times, `index` is: 0, 1, 2, 3
}

You can iterate over the elements of an array or set:

let list = ["a", "b", "c"]
for item in list {
  // `item` contains the element value
}

And on the elements of a dictionary:

let list = ["a": 1, "b": 2, "c": 2]
for (key, value) in list {
  // `key` contains the item key
  // `value` contains the item value
}

while loops in Swift

A while loop can be used to iterate on anything, and will run while the condition is true:

while [condition] {
    //statements...
}

The condition is checked at the start, before the loop block is executed.

Example:

var item = 0
while item <= 3 { //repeats 3 times
    print(item)
    item += 1
}

repeat-while loops in Swift

A repeat-while loop in Swift is similar to the while loop. But in this case the condition is checked at the end, after the loop block, so the loop block is executed at least once. Then the condition is checked, and if it is evaluated as true, the loop block is repeated:

repeat {
    //statements...
} while [condition]

Example:

var item = 0
repeat { //repeats 3 times
    print(item)
    item += 1
} while item < 3

continue and break statements in Swift

Swift provides you 2 statements that you can use to control the flow inside a loop: continue and break.

You use continue to stop the current iteration, and run the next iteration of the loop.

break ends the loop, not executing any other iteration.

Example:

let list = ["a", "b", "c"]
for item in list {
  if (item == "b") {
    break
  }
  //do something
}

How to Write Comments in Swift

A comment in Swift can take 2 forms: a single-line comment, and a multi-line comment.

A single-line comment looks like this:

//this is a comment

and and you can put it at the end of a line of code:

let a = 1 //this is a comment

A multi-line comment is written using this syntax:

/* this
 is
    a multi-line
 comment
*/

Swift allows you to nest multi-line comments:

/* this
 is
    a /* nested */ multi-line
 comment
*/

This is handy especially when commenting out large portions of code that already contain multi-line comments.

Semicolons in Swift

In Swift, semicolons are generally optional.

You can write statements on separate lines, and you don't need to add a semicolon:

let list = ["a", "b", "c"]
var a = 2

You can add a semicolon, but it adds nothing meaningful in this case:

let list = ["a", "b", "c"];
var a = 2;

But if you want to write more than one statement on the same line, then you need to add a semicolon:

var a = 2; let b = 3

Numbers in Swift

In Swift, numbers have 2 main types: Int and Double.

An Int is a number without decimal point. A Double is a number with decimal point.

Both use 64 bits, on modern computers that work with 64 bits, and 32 bit on 32-bit platforms.

The range of values they can store depends on the platform used, and can be retrieved using the int property of each type:

Range of int values

Then, in addition to Int and Double, we have lots of other numeric types. These were mostly used to interact with APIs built in the past and that needed to interact with C or Objective-C, and you must be aware that we have them:

• Int8 is an integer with 8 bits
• Int16 is an integer with 16 bits
• Int32 is an integer with 32 bits
• Int64 is an integer with 64 bits
• UInt8 is an unsigned integer with 8 bits
• UInt16 is an unsigned integer with 16 bits
• UInt32 is an unsigned integer with 32 bits
• UInt64 is an unsigned integer with 64 bits
• UInt is like Int, but unsigned, and it ranges from 0 to Int.max * 2.
• Float is a decimal number with 32 bits.

Then using Cocoa APIs you might use other numeric types like CLong, CGFloat, and more.

You will always use Int or Double in your code, and use those specific types only in particular cases.

Remember that you can always convert any of those types to Int and Double types, instantiating a number passing the value inside parentheses to Double() or Int():

let age : UInt8 = 3
let intAge = Int(age)

You can also convert a number from Double to Int:

let age = Double(3)
let count = Int(3.14)

How to convert a number from Double to Int

Strings in Swift

Strings are one of the most popular tools in programming.

In Swift, you can define a string using the string literal syntax:

let name = "Roger"

We use double quotes. Single quotes are not valid string delimiters.

A string can span over multiple lines using 3 double quotes:

let description = """
    a long
      long 
          long description
    """

You can use string interpolation to embed an expression in a string:

let age = 8

let name = """
    Roger, age \(age)
    Next year he will be \(age + 1)
    """

You can concatenate two strings with the + operator:

var name = "Roger"
name = name + " The Dog"

And you can append text to a string with the += operator:

var name = "Roger"
name += " The Dog"

Or using the append(_:) method:

var name = "Roger"
name.append(" The Dog")

You can count the characters in a string using the count string property:

let name = "Roger"
name.count //5

Any string comes with a set of useful methods, for example:

• removeFirst() to remove the first character
• removeLast() to remove the last character
• lowercased() to get a new string, lowercased
• uppercased() to get a new string, uppercased
• starts(with:) which returns true if the string starts with a specific substring
• contains() which returns true if the string contains a specific character

and many, many more.

When you need to reference an item in the string, since strings in Swift are unicode, we can't simply reference the letter o in let name = "Roger" using name[1]. You need to work with indexes.

Any string provides the starting index with the startIndex property:

let name = "Roger"
name.startIndex //0

To calculate a specific index in the string, you calculate it using the index(i:offsetBy:) method:

let name = "Roger"
let i = name.index(name.startIndex, offsetBy: 2)
name[i] //"g"

You can also use the index to get a substring:

let name = "Roger"
let i = name.index(name.startIndex, offsetBy: 2)
name.suffix(from: i) //"ger"

//Or using the subscript:

name[i...] //"ger"

When you get a substring from a string, the type of the result is Substring, not String.

let name = "Roger"
let i = name.index(name.startIndex, offsetBy: 2)
print(type(of: name.suffix(from: i))) 
//Substring

Substrings are more memory efficient, because you do not get a new string, but the same memory structure is used behind the scenes. But you need to be careful when you deal with strings a lot, as there are optimizations you can implement.

Strings are collections, and they can be iterated over in loops.

Booleans in Swift

Swift provides the Bool type, which can have two values: true and false.

var done = false
done = true

Booleans are especially useful with conditional control structures like if statements or the ternary conditional operator:

var done = true

if done == true {
    //code
}

Arrays in Swift

We use arrays to create a collection of items.

In this example we create an array holding 3 integers:

var list = [1, 2, 3]

We can access the first item using the syntax list[0], the second using list[1], and so on.

Elements in an array in Swift must have the same type.

The type can be inferred if you initialize the array at declaration time, like in the case above.

Otherwise the type of values an array can include must be declared, in this way:

var list: [Int] = []

Another shorthand syntax is:

var list = [Int]()

You can also explicitly declare the type at initialization, like this:

var list: [Int] = [1, 2, 3]

A quick way to initialize an array is to use the range operator:

var list = Array(1...4) //[1, 2, 3, 4]

To get the number of items in the array, use the count property:

var list = [1, 2, 3]
list.count //3

If an array is empty, its isEmpty property is true.

var list = [1, 2, 3]
list.isEmpty //false

You can append an item at the end of the array using the append() method:

var list: [Int] = [1, 2, 3]
list.append(4)

or you can insert an item at any position of the array using insert(newElement: <Type> at: Int):

var list: [Int] = [1, 2, 3]
list.insert(17, at: 2)
//list is [1, 2, 17, 3]

An array must be declared as var to be modified. If it's declared with let, you cannot modify it by adding or removing elements.

To remove one item from the array, use remove(at:) passing the index of the element to remove:

var list: [Int] = [1, 2, 3]
list.remove(1)
//list is [1, 3]

removeLast() and removeFirst() are two handy ways to remove the last and first element.

To remove all items from the array, you can use removeAll() or you can assign an empty array:

var list: [Int] = [1, 2, 3]
list.removeAll()
//or
list = []

The sort() method sorts the array:

var list = [3, 1, 2]
list.sort()
//list is [1, 2, 3]

There are a lot more methods, but those are the basic ones.

Arrays are equal when they contain the same elements, of the same type:

[1, 2, 3] == [1, 2, 3] //true

Arrays are passed by value, which means if you pass an array to a function, or return it from a function, the array is copied.

Arrays are collections, and they can be iterated over in loops.

Sets in Swift

You use sets to create collections of non-repeated items.

While an array can contain many times the same item, you only have unique items in a set.

You can declare a set of Int values in this way:

let set: Set<Int> = [1, 2, 3]

or you can initialize it from an array:

let set = Set([1, 2, 3])

You can add items to the set using insert():

var set = Set([1, 2, 3])
set.insert(17)

Unlike arrays, there is no order or position in a set. Items are retrieved and inserted randomly.

The way to print the content of a set so it's ordered is to transform it into an array using the sorted() method:

var set = Set([2, 1, 3])
let orderedList = set.sorted()

To check if a set contains an element, use the contains() method:

var set = Set([1, 2, 3])
set.contains(2) //true

To get the number of items in the set, use the count property:

let set = Set([1, 2, 3])
set.count //3

If a set is empty, its isEmpty property is true.

let set = Set([1, 2, 3])
set.isEmpty //false

To remove one item from the array, use remove() passing the value of the element:

var set = Set([1, 2, 3])
set.remove(1)
//set is [2, 3]

To remove all items from the set, you can use removeAll():

set.removeAll()

Sets, like arrays, are passed by value. This means that if you pass it to a function, or return it from a function, the set is copied.

Sets are great to perform set math operations like intersection, union, subtracting, and more.

These methods help with this:

• intersection(_:)
• symmetricDifference(_:)
• union(_:)
• subtracting(_:)
• isSubset(of:)
• isSuperset(of:)
• isStrictSubset(of:)
• isStrictSuperset(of:)
• isDisjoint(with:)

Sets are collections, and they can be iterated over in loops.

Dictionaries in Swift

We use dictionaries to create a collection of key-value pairs.

Here is how to create a dictionary with 1 key-value pair, where the key is a String and the value is an Int:

var dict = ["Roger": 8, "Syd": 7]

In this case the type is inferred. You can also explicitly set the type at declaration time:

var dict: [String: Int] = ["Roger": 8, "Syd": 7]

In this example we create an empty dictionary of Int keys and String values:

var dict = [String: Int]()

//or

var dict: [String: Int] = [:]

You can access the value assigned to a key using this syntax:

var dict = ["Roger": 8, "Syd": 7]

dict["Roger"] //8
dict["Syd"] //7

You can change the value assigned to a key in this way:

dict["Roger"] = 9

A dictionary must be declared as var to be modified. If it's declared with let, you cannot modify it by adding or removing elements.

Use the same syntax to add a new key/value pair:

dict["Tina"] = 4

To remove a key/value pair, assign the value to nil:

dict["Tina"] = nil

Or call the removeValue(forKey:) method:

dict.removeValue(forKey: "Tina")

To get the number of items in the dictionary, use the count property:

var dict = ["Roger": 8, "Syd": 7]
dict.count //2

If a dictionary is empty, its isEmpty property is true.

var dict = [String: Int]()
dict.isEmpty //true

There are a lot of methods related to dictionaries, but those are the basic ones.

Dictionaries are passed by value, which means if you pass it to a function, or return it from a function, the dictionary is copied.

Dictionaries are collections, and they can be iterated over in loops.

Tuples in Swift

You use tuples to group multiple values into a single collection. For example you can declare a variable dog containing a String and an Int value:

let dog : (String, Int)

And you can initialize them with a name and an age

let dog : (String, Int) = ("Roger", 8)

But as with any other variable, the type can be inferred during initialization:

let dog = ("Roger", 8)

You can use named elements:

let dog = (name: "Roger", age: 8)

dog.name //"Roger"
dog.age //8

Once a tuple is defined, you can decompose it to individual variables in this way:

let dog = ("Roger", 8)
let (name, age) = dog

and if you need to just get one of the values, you can use the special underscore keyword to ignore the other ones:

let dog = ("Roger", 8)
let (name, _) = dog

Tuples are an awesome tool for various needs.

The most obvious one is that they're a short way to group similar data.

Another one of those needs is returning multiple items from a function. A function can only return a single item, so a tuple is a convenient structure for that.

Another handy functionality allowed by tuples is swapping elements:

var a = 1
var b = 2

(a, b) = (b, a)

//a == 2
//b == 1

Optionals and nil in Swift

Optionals are one key feature of Swift.

When you don't know if a value will be present or absent, you declare the type as an optional.

The optional wraps another value with its own type. Or maybe not.

We declare an optional by adding a question mark after its type, like this:

var value: Int? = 10

Now value is not an Int value. It's an optional wrapping an Int value.

To find out if the optional wraps a value, you must unwrap it.

You do so using an exclamation mark:

var value: Int? = 10
print(value!) //10

Swift methods often return an optional. For example the Int type initializer accepts a string, and returns an Int optional:

Int type initializer takes in a string and returns an int optional

This is because it does not know if the string can be converted to a number.

If the optional does not contain a value, it evaluates as nil, and you cannot unwrap it:

Evaluating to nil

nil is a special value that cannot be assigned to a variable. Only to an optional:

You can only assign nil to an optional (not an int)

You typically use if statements to unwrap values in your code, like this:

var value: Int? = 2

if let age = value {
    print(age)
}

Enumerations in Swift

Enumerations are a way to group a set of different options under a common name.

Example:

enum Animal {
    case dog
    case cat
    case mouse
    case horse
}

This Animal enum is now a type.

A type whose value can only be one of the cases listed.

If you define a variable of type Animal:

var animal: Animal

you can later decide which value to assign it using this syntax:

var animal: Animal
animal = .dog

We can use enumerations in control structures like switches:

enum Animal {
    case dog
    case cat
    case mouse
    case horse
}

let animal = Animal.dog

switch animal {
case .dog: print("dog")
case .cat: print("cat")
default: print("another animal")
}

Enumeration values can be strings, characters, or numbers.

You can also define an enum on a single line:

enum Animal {
    case dog, cat, mouse, horse
}

And you can also add type declaration to the enumeration, and each case has a value of that type assigned:

enum Animal: Int {
    case dog = 1
    case cat = 2
    case mouse = 3
    case horse = 4
}

Once you have a variable, you can get this value using its rawValue property:

enum Animal: Int {
    case dog = 1
    case cat = 2
    case mouse = 3
    case horse = 4
}

var animal: Animal
animal = .dog

animal.rawValue //1

Enumerations are a value type. This means they are copied when passed to a function, or when returned from a function. And when we assign a variable pointing to an enumeration to another variable.

Structures in Swift

Structures are an essential Swift concept.

Structures are everywhere in Swift. Even the built-in types are structures.

We can create instances of structures, which we call objects.

In most languages, objects can only be created from classes. Swift has classes, too, but you can create objects also from structures. The official documentation actually advises that you should prefer structures because they are easier to use.

Structures are a light versions of classes.

A struct can:

• have properties
• have methods (functions)
• define subscripts
• define initializers
• conform to protocols
• be extended

One important thing classes allow is inheritance, so if you need that, you have classes.

A struct is defined using this syntax:

struct Dog {

}

Inside a structure you can define stored properties:

struct Dog {
    var age = 8
    var name = "Roger"
}

This structure definition defines a type. To create a new instance with this type, we use this syntax:

let roger = Dog()

Once you have an instance, you can access its properties using the dot syntax:

let roger = Dog()
roger.age
roger.name

The same dot syntax is used to update a property value:

roger.age = 9

You can also create a struct instance by passing the values of the properties:

let syd = Dog(age: 7, name: "Syd")
syd.age
syd.name

To do so, properties must be defined variables with var, not as constants (with let). It's also important to respect the order those properties are defined.

Structures can have instance methods: functions that belong to an instance of a structure.

struct Dog {
    var age = 8
    var name = "Roger"
    func bark() {
        print("\(name): wof!")
    }
}

And we also have type methods:

struct Dog {
    var age = 8
    var name = "Roger"
    func bark() {
        print("\(name): wof!")
    }
    static func hello() {
        print("Hello I am the Dog struct")
    }
}

This is invoked as Dog.hello().

Structures are a value type. This means they are copied when passed to a function, or when returned from a function. And when we assign a variable pointing to a structure to another variable.

This also means that if we want to update the properties of a structure we must define it using var and not let.

All types in Swift are defined as structures: Int, Double, String, arrays and dictionaries, and more are structures.

Classes in Swift

Classes are a bit similar to structures, but they have some key differences.

A class is defined using this syntax:

class Dog {

}

Inside a class you can define stored properties:

class Dog {
    var age = 0
}

A class definition defines a type. To create a new instance with this type, we use this syntax:

let roger = Dog()

Once you have an instance, you can access its properties using the dot syntax:

let roger = Dog()
roger.age

You use the same dot syntax to update a property value:

roger.age = 9

One big difference is that classes are reference types. Structures (and enumerations) are value types.

This means that assigning a class instance to another variable does not copy the instance. Both variables point to the same instance:

class Dog {
    var age = 0
}

let roger = Dog()
let syd = roger

roger.age = 9
//syd.age == 9

This also means we can define a reference to a class using let, and we can change its properties, as you saw in the example above.

We can create instances of classes, and we call them objects.

As with structs, classes can have properties, methods, and more.

Contrary to structs, we must define an initializer in order to initialize the values when we create an instance:

class Dog {
    var age : Int

    init(age: Int) {
        self.age = age
    }
}

let roger = Dog(age: 9)

You can only declare properties without initializing them if you have an initializer.

See the use of self. We need it because age is both an instance property and the init(age:) method parameter. self.age references the age instance property.

Classes can have instance methods: functions that belong to an instance of a class.

class Dog {
    var age = 8
    var name = "Roger"

    func bark() {
      print("\(name): wof!")
    }
}

And we also have type methods:

class Dog {
    var age = 8
    var name = "Roger"

    func bark() {
        print("\(name): wof!")
    }
    static func hello() {
        print("Hello I am the Dog struct")
    }
}

Invoked as Dog.hello().

One important thing classes allow is inheritance.

A class can inherit all the properties and methods from another class.

Say we have a class Animal. Every animal has an age:

class Animal {
    var age: Int
}

Not every animal has a name. Dogs have a name. So we create a Dog class extending from Animal:

class Dog: Animal {
    var name: String
}

Now we must add an initializer for both classes. In the Dog case, after we do the class-specific initialization, we can call the parent class initializer using super.init():

class Animal {
    var age: Int

    init(age: Int) {
        self.age = age
    }
}

class Dog: Animal {
    var name: String

    init(age: Int, name: String) {
        self.name = name
        super.init(age: age)
    }
}

var horse = Animal(age: 8)
var roger = Dog(age: 8, name: "Roger")

Animal is now a superclass, and Dog is a subclass.

There's more to say about classes, but this is a good introduction.

Functions in Swift

Your program's code is organized into functions.

You can declare a function using the func keyword:

func bark() {
    print("woof!")
}

Functions can be assigned to structures, classes and enumerations, and in this case we call them methods.

A function is invoked using its name:

bark()

A function can return a value:

func bark() -> String {
    print("woof!")
      return "barked successfully"
}

And you can assign it to a variable:

let result = bark()

A function can accept parameters. Each parameter has a name and a type:

func bark(times: Int) {
    for index in 0..<times {
        print("woof!")
    }
}

The name of a parameter is internal to the function.

We use the name of the parameter when we call the function to pass in its value:

bark(times: 3)

When we call the function we must pass all the parameters defined.

Here is a function that accepts multiple parameters:

func bark(times: Int, repeatBark: Bool) {
    for index in 0..<times {
        if repeatBark == true {
            print("woof woof!")
        } else {
            print("woof!")
        }            
    }
}

In this case you call it in this way:

bark(times: 3, repeat: true)

When we talk about this function, we don't call it bark(). We call it bark(times:repeat:).

This is because we can have multiple functions with the same name, but different set of parameters.

You can avoid using labels by using the _ keyword:

func bark(_ times: Int, repeatBark: Bool) {
    //...the function body
}

So you can invoke it in this way:

bark(3, repeat: true)

It's common in Swift and iOS APIs to have the first parameter with no label, and the other parameters labeled.

It makes for a nice and expressive API, when you design the names of the function and the parameters nicely.

You can only return one value from a function. If you need to return multiple values, it's common to return a tuple:

func bark() -> (String, Int) {
    print("woof!")
      return ("barked successfully", 1)
}

And you can assign the result to a tuple:

let (result, num) = bark()

print(result) //"barked successfully"
print(num) //1

You can nest functions inside other functions. When this happens, the inner function is invisible to outside the outer function.

Protocols in Swift

A protocol is a way to have different objects, of different types, have a common set of functionalities.

You define a protocol like this:

protocol Mammal {

}

Structs and classes can adopt a protocol in this way:

struct Dog: Mammal {

}

class Cat: Mammal {

}

A protocol can define properties and methods, without providing values and implementations, and a struct/class must implement them:

protocol Mammal {
    var age: Int { get set }
    func walk()
}

The property can be defined as get or get set. If it's get, the property must be implemented as read only, with a getter.

Any type that adopts the protocol must conform to the protocol by implementing those methods or providing those properties:

struct Dog: Mammal {
    var age: Int = 0
    func walk() {
        print("The dog is walking")
    }
}

class Cat: Mammal {
    var age: Int = 0
    func walk() {
        print("The cat is walking")
    }
}

Structs and classes can adopt multiple protocols:

struct Dog: Mammal, Animal {

}

class Cat: Mammal, Animal {

}

Notice that for classes, this is the same syntax used to define a superclass. If there is a superclass, list it as the first item in the list, after the colon.

Where to Go From Here

I hope this little handbook was useful in shining a light on how to get started with Swift. And I hope you are now interested to learn more about it!

I can now point you to a few places to learn more:

• The official Swift Language Guide
• The Swift Standard Library
• WWDC Swift videos

You can get a PDF and ePub version of this Swift Beginner's Handbook here.

In this article we will talk about why and how to implement the GameCenter's Leaderboard within your app.

Why GameCenter is Making a Huge Revival

You can make iPhone games without a scoreboard, but leaderboards can help make the game feel more competitive, like people are competing against one another around the World.

Instead of creating and managing your own backend, the GameCenter Leaderboard allows you to scale with traffic infinitely, skip an entire login page for authorization, get the Image, Name, and friends playing the same game – all without your users having to enter anything.

Especially with iOS 16, Apple is investing more in improving it, and driving more app usage, like through Push Notifications when your friend beats your score in the game.

In my journey of learning SwiftUI, I have been creating and publishing apps, because IMO that's the best way to learn.

There wasn't much updated documentation on how to do a lot of this, especially none with SwiftUI nor with the advent of async and await in Swift. So I consolidated and simplified it for everyone to build amazing apps. So feel free to invite me to test your apps too!

Pre-Requisites:

• You'll need to have an Apple Developer paid account
• You have to create the App Id for your app in the provisioning profiles section of the Apple Developer Portal
• You have to create the App in the iTunes Connect Connect portal

How to Implement Your iOS Leaderboard in 6 Steps

Most of the code logic for the leaderboard is in this file if you want to skip ahead. Here's the steps as follows:

1. How to Create the App Store Connect Leaderboard

Screenshot from the Apple iTunes Connect Portal

Once you have created the app in the App Store Connect portal successfully, go to the Services tab for the app -> and make sure you're in the GameCenter page.

Then add a new leaderboard using the "+" sign, which can either be "Classic" (scores never reset) or "Recurring" (scores reset based on your frequency settings).

Most games prefer a recurring leaderboard so that the leaderboard isn't cluttered with older impossible to reach high scores.

The LeaderboardID you input there is the one that you need to use in all the places in the code that ask for it.

Details required to create a new Leaderboard

2. How to Set Up GameCenter Authentication

First, you'll need to authenticate users to GameCenter in order for any of this functionality to work.

So we'll use this code to do that, which basically makes sure that you (GKLocalPlayer.local) are authenticated, or prints an error if there is one:

func authenticateUser() {
    GKLocalPlayer.local.authenticateHandler = { vc, error in
        guard error == nil else {
            print(error?.localizedDescription ?? "")
            return
        }
    }
}

If the user is authenticated, you will see a little popup in the UI. If not, the user will be taken to a page to login to their GameCenter account.

A sign that displays when a user is logged in

3. How to Display Leaderboard Items in the UI

In order to get the data away from the GameCenter ViewController leaderboards (GKLeaderboard), you need to use the loadLeaderboards .

You can switch up the loadEntries function from .global to .friends in order to only pull your friends.

You can also retrieve the image for each player by iterating over each player and performing a loadPhoto.

Using NSRang(1...5), you can choose how many players to display. This pulls the users with the highest 5 scores from the leaderboard and returns none if there's no users, such as in the case when the cycle refreshes for a recurring Leaderboard.

This is what pulling data from a leaderboard could look like if you take advantage of async-await:

func loadLeaderboard() async {
    playersList.removeAll()
    Task{
        var playersListTemp : [Player] = []
        let leaderboards = try await GKLeaderboard.loadLeaderboards(IDs: [leaderboardIdentifier])
        if let leaderboard = leaderboards.filter ({ $0.baseLeaderboardID == self.leaderboardIdentifier }).first {
            let allPlayers = try await leaderboard.loadEntries(for: .global, timeScope: .allTime, range: NSRange(1...5))
            if allPlayers.1.count > 0 {
                try await allPlayers.1.asyncForEach { leaderboardEntry in
                    var image = try await leaderboardEntry.player.loadPhoto(for: .small)
                    playersListTemp.append(Player(name: leaderboardEntry.player.displayName, score:leaderboardEntry.formattedScore, image: image))
                                print(playersListTemp)
                    playersListTemp.sort{
                        $0.score < $1.score
                    }
                }
            }
        }
        playersList = playersListTemp            
    }
}

You can get leaderboard data into your app

4. How to Call Functionality in SwiftUI as the View/Page Appears

You can take advantage of the onAppear lifecycle function of the view to actually make the calls to authenticate and load, but you can also do it on the tap of a button if you prefer that:

.onAppear(){
    if !GKLocalPlayer.local.isAuthenticated {
        authenticateUser()
    } else if playersList.count == 0 {
        Task{
            await loadLeaderboard()
        }
    }
}

5. How to Load the Submitted Scores

In order to load the scores, you need to submit them as well. The submitScore function can help you with that.

• The flightsClimbed variable should contain the score that you would like to submit.
• GameKit makes sure to only display your best score for the life of the leaderboard.
• The leaderboardId contains the value that you manually enter in your App Store Connect account:

func leaderboard() async{
    Task{
        try await GKLeaderboard.submitScore(
            flightsClimbed,
            context: 0,
            player: GKLocalPlayer.local,
            leaderboardIDs: ["com.tfp.stairsteppermaster.flights"]
        )
    }
    calculateAchievements()
}

6. How to display the GameCenter ViewController Portal

When you're logged into GameCenter, a little annoying icon appears in the top right of your screen. When you tap on it, you are taken to the GameCenter ViewController. Luckily you can hide it if it's not part of your design, using GKAccessPoint.shared.isActive = false.

Since the GameCenter UI is a UIKit ViewController and not a simple SwiftUI View, you need to create this UIViewControllerRepresentable first (as you can see here), to launch GameCenter using a different button,

Once you add that file to your project, you can display the GameCenter portal simply using this: GameCenterView(format: gameCenterViewControllerState) where gameCenterViewControllerState can be help you go to a detail page in GameCenter.

GameCenter's Leaderboard View

Things to Keep in Mind While using GameCenter's Leaderboards:

• Simulator Debugging – For some reason the authenticate to GameCenter is extremely slow on a simulator, so it might make sense to even create a mock of data when using the simulator.
• Challenges – You can't programmatically issue GameKit Challenges to your friends anymore due to deprecation. Instead, you have to do those manually within the user's GameCenter dashboard against GameKit Achievements. Also, there's no way to view challenges you have sent.
• Achievements – Leaderboards are different from the GameKit Achievements, which is calculated and displayed differently, but a lot easier. Those can also be pulled into the app as well, as you can see below:

GameKit Challenges and Achievements

Wrapping Up

You can try out the free open-source Stair Master Climber iPhone Health & Fitness app that I shared above. I would love to know what you think so that we can learn together.

Feel free to reach out to me on social media or by email if you have any questions.

Hello everyone! In this article we are going to learn how to use UISearchController in iOS Apps.

What are we going to build?

We are going to build a movie search application which uses the TMDB API to fetch movie info and display it using a UICollectionView based on a user's search query.

Project Setup

Open up Xcode and create a new blank iOS App project – make sure you select UIKit and not SwiftUI.

In this app we are going to use the MVC Pattern so organise the project by creating the following groups and Swift files:

Now close your Xcode project. Open up the terminal and move to your project directory. Here we need to add SD WebImage Cocoa Pods to asynchronously download and cache the movie poster images.

Type the following command in the terminal:

pod init

Now when you list the contents of the directory, you can see that there is a new Podfile. Open the file using any text editor (here I've used Vim). Edit your Podfile so that it looks similar to the below image. Save and close the Podfile.

Now that we have specified the SD WebImage, we can install the dependencies by running the below command:

pod install

As you can see, we have successfully added the SD WebImage pod in our iOS project. Now run the below command to open our project in Xcode.

open PROJECT_NAME.xcworkspace

After opening Xcode, make sure you build your project by hitting Command+B.

How to Design the User Interface using UIKit and Programmatic UI

Our app needs three UIElements navigation bars to hold the search bar, UISearchBarController for actual search, and a UICollectionView to display the search results.

Open up your Scenedelegate.swift file and add the following code inside it which will connect to the session method:

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        guard let scene = (scene as? UIWindowScene) else { return }
        window = UIWindow(windowScene: scene)       window?.rootViewController=UINavigationController(rootViewController:HomeVC())
        window?.makeKeyAndVisible()
    }

Since we are using a programatic UI, first we need to mention our Root View controller – that is, the first screen which will be displayed when the user launches the app.

Here in this app we're using only one View Controller, so we wrap it inside a UINavigationController. This provides a navigation bar where we can place our UISearchController.

Open up the HomeVC.swift file and add the following properties:

 private var SearchBar: UISearchController = {
        let sb = UISearchController()
        sb.searchBar.placeholder = "Enter the movie name"
        sb.searchBar.searchBarStyle = .minimal
        return sb
    }()

    private var MovieCollectionView: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .vertical
        layout.itemSize = CGSize(width: UIScreen.main.bounds.width/3 - 10, height: 200)
        let cv = UICollectionView(frame: .zero, collectionViewLayout: layout)
        cv.register(MovieCell.self, forCellWithReuseIdentifier: MovieCell.ID)
        return cv
    }()

First we create our UISearchController and configure its properties such as placeholder text and style.

Then we create a UICollectionView and specify the type of layout our collection view should use. In this case it is UICollectionViewFlowLayout and other properties such as scroll direction, item size, and specifying a custom CollectionView cell class which we will create later in our project.

Inside the HomeVC class create a new function and add the following code to configure auto-layout constraints programmatically for our UICollectionView:

    //MARK: - HELPERS
    func configureUI(){
        MovieCollectionView.translatesAutoresizingMaskIntoConstraints = false
        MovieCollectionView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        MovieCollectionView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        MovieCollectionView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
        MovieCollectionView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
    }

First we say that we don't need to convert the auto resizing mask into the constraints. Then we pin our collection view to all four sides of our View Controller.

Inside the viewDidLoad() method add the following lines of code:

  override func viewDidLoad() {
        super.viewDidLoad()

        navigationItem.title  = "Movie Search"
        view.backgroundColor = .systemBackground
        SearchBar.searchResultsUpdater = self
        navigationItem.searchController = SearchBar
        view.addSubview(MovieCollectionView)
        MovieCollectionView.delegate = self
        MovieCollectionView.dataSource = self
        configureUI()
    }

Here we first specify the title for our ViewController followed by the background color which is the systemBackground color. If the device is in light mode it shows a white background. If it is in dark mode, then it shows a dark background.

Then we set current the view controller as the search result updater, then add our SearchController to the navigation bar, add the UICollectionView to the ViewController, and setup delegate and datasource. Finally we pin the UICollectionView by using auto-layout.

Create an extension for HomeVC and implement the UISearchResultsUpdating protocol and its stub method updateSearchResults.

extension HomeVC: UISearchResultsUpdating{

    func updateSearchResults(for searchController: UISearchController) {
        guard let query = searchController.searchBar.text else{return}

        }

    }


}

The updateSearchResults() method will be called whenever the text entered in the search bar changes or when the user taps the search button on their keyboard.

Next we need to create that custom UICollectionView cell. Inside the MovieCell.swift file, add the following code:

import Foundation
import UIKit
import SDWebImage

class MovieCell: UICollectionViewCell{

    static let ID = "MovieCell"
    private var MoviePosterImageView: UIImageView = {
        let imageView = UIImageView()
        imageView.contentMode = .scaleAspectFit
      //  imageView.image = UIImage(systemName: "house")
        return imageView
    }()

    override init(frame: CGRect) {
        super.init(frame: frame)
        addSubview(MoviePosterImageView)
        configureUI()
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}

extension MovieCell{
    func configureUI(){
        MoviePosterImageView.translatesAutoresizingMaskIntoConstraints = false
        MoviePosterImageView.topAnchor.constraint(equalTo: topAnchor).isActive = true
        MoviePosterImageView.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
        MoviePosterImageView.leftAnchor.constraint(equalTo: leftAnchor).isActive = true
        MoviePosterImageView.rightAnchor.constraint(equalTo: rightAnchor).isActive = true
    }
    func updateCell(posterURL: String?){
        if let posterURL = posterURL {
            guard let CompleteURL = URL(string: "https://image.tmdb.org/t/p/w500/\(posterURL)") else {return}
            self.MoviePosterImageView.sd_setImage(with: CompleteURL)
        }

    }
}

Here we create our custom collection view cell by sub-classing the UICollectionView class and implementing the init() functions.

We create a UIImageView to display the movie poster image and setup auto-layout constraints for it. Then we create a user defined function which takes the Movie poster URL string a parameter and downloads it asynchronously without affecting the UI Thread/Main thread. It does this by using the SD WebImage CocoaPod which we added earlier.

How to Set Up Our API

Before moving on, you'll need to get your API key for the TMDB API by creating an account (it's free). We are going to use the Movie Search end point of the API which takes the API Key and movie name as parameters.

https://api.themoviedb.org/3/search/movie?api_key=API_KEY_HERE&query=batman

You can examine the API response by running it in Postman.

How to Create a Model for the API Response

Now we get a JSON response from the API. We need to decode them to Swift which we can do by creating a model struct that implements the Codable protocol.

WE can generate the model struct for our JSON response easily by using JSON to Swift websites. Here is the model code for the API response – you can just copy and paste it inside the Model.swift file:

import Foundation

struct TrendingTitleResponse: Codable {
    let results: [Title]
}

struct Title: Codable {
    let id: Int
    let media_type: String?
    let original_name: String?
    let original_title: String?
    let poster_path: String?
    let overview: String?
    let vote_count: Int
    let release_date: String?
    let vote_average: Double
}

struct YoutubeSearchResponse: Codable {
    let items: [VideoElement]
}


struct VideoElement: Codable {
    let id: IdVideoElement
}


struct IdVideoElement: Codable {
    let kind: String
    let videoId: String
}

How to Perform HTTP Requests Using Swift

Now we need to write some Swift code to perform HTTP GET requests which return the JSON response of the API.

Swift provides a URLSession class which makes it easier to write networking code without needing any third party libraries like AFNetworking, AlamoFire, and so on.

Open APIService.swift and add the following code:

import Foundation

class APIService{
    static var shared = APIService()
    let session = URLSession(configuration: .default)

    func getMovies(for Query: String,completion:@escaping([Title]?,Error?)->Void){
        guard let FormatedQuery = Query.addingPercentEncoding(withAllowedCharacters: .urlHostAllowed)  else{return}

        guard let  SEARCH_URL = URL(string: "https://api.themoviedb.org/3/search/movie?api_key=API_KEY_HERE&query=\(FormatedQuery)") else {print("INVALID")
            return}



        let task = session.dataTask(with: SEARCH_URL) { data, response, error in
            if let error = error {
                print(error.localizedDescription)
                completion(nil,error)
            }
            if let data = data {
                do{
                    let decodedData = try JSONDecoder().decode(TrendingTitleResponse.self, from: data)
                 //   print(decodedData)
                    completion(decodedData.results,nil)
                }
                catch{
                    print(error)
                }
            }
        }
        task.resume()
    }
}

Here we created a class named API Service with the singleton pattern so we need an instance for this class as a static member of the class. Then we created a session for our networking task with the default configuration, followed by a user defined method getMovies().

Then we created our networking task – in this case we need to perform HTTP GET requests which can be performed using the dataTask() method of the URLSession class. It takes the URL as a parameter and gives a completion handler which contains data returned from the API, error data if any error has occurred, and a response which has HTTP Response information such as status codes and their corresponding messages.

If there is any error, then we escape out of this function with error data. If not, then we decode our JSON data based on our Swift Model and escape out of this function with the decoded data.

How to Display the Search Results on the UICollectionView

In HomeVC.swift, create a private property which is an array of Title objects. These will hold each movie's info returned by the API.

private var Movies = [Title]()

In HomeVC.swift create an extension for the HomeVC class and implement the UIColletionViewDelegate and UICollectionViewDatasource protocols. Then implement numberOfItemsInSection (which is equal to the number of movies returned by the API) and cellForItemAt (which actually populates the cell with API responses, like download and set the poster image).

 func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return Movies.count
    }
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        if let cell = collectionView.dequeueReusableCell(withReuseIdentifier: MovieCell.ID, for: indexPath) as? MovieCell{
           // cell.backgroundColor = .systemBackground

            cell.updateCell(posterURL: Movies[indexPath.row].poster_path)
            return cell
        }
        return UICollectionViewCell()

    }

Finally we need to make actual API call which we do inside the updateSearchResults() delegate method which we have implemented previously. Inside that method add the following code:

    func updateSearchResults(for searchController: UISearchController) {
        guard let query = searchController.searchBar.text else{return}
        APIService.shared.getMovies(for:query.trimmingCharacters(in: .whitespaces)) { titles, error in
            if let titles = titles {
                self.Movies = titles
                DispatchQueue.main.async {
                    self.MovieCollectionView.reloadData()
                }

            }
        }

    }

Here, whenever the user types in the search bar or presses the search button, we make an HTTP GET request to fetch a movie (based on the name entered in the search bar). Then we reload the CollectionView which updates the collection view cells with the movie poster.

Note that we need to do this in the Main Thread/UI Thread, because by default iOS automatically makes HTTP request in background thread. This means that we need to use UI/Main Thread to update our UI elements.

Now run your app in the simulator to see the result:

Congratulations! You have learned to use UISearchController in iOS apps.

We just published a 5-hour course on the freeCodeCamp.org YouTube channel that will teach you how to use Swift 5, UIKit, and Xcode to develop iOS apps by building a Netflix clone.

Amr created this course. Amr is an iOS developer who has created many popular tutorials.

In this course you will learn how to implement the MVVM design pattern and create the app from scratch in Xcode. The Netflix code will play videos using the YouTube API.

Here are the sections in this course:

• Introduction and App Demo
• Creating new Xcode Project
• Creating MainTabBarViewController
• Setting HomeViewController TableView
• Setting home TableViewCell and it’s CollectionView
• Creating Table’s HeaderView
• Customizing the navigation bar
• Setting Tableview sections titles
• Sending URL Requests and Parsing JSON response
• Using Extensions
• Consuming API To Fetch Data for each Section
• Refactoring Models
• Creating Custom CollectionViewCell
• Passing data to the CollectionView
• Viewing poster images inside CollectionViewCell
• Creating Upcoming TableView inside Upcoming Tab
• Creating custom TableViewCell from the upcoming table
• Creating TitleViewModel
• Creating Top Search TableView inside TopSearch tab
• Creating SearchResultsViewController to display search results
• Querying database for individual movie
• Using YouTube API
• Parsing YouTube API Response
• Handling selections of cells (Tapping on cells)
• Creating TitlePreviewViewController
• Refactoring TableViewHeader Hero title
• Handling Tapping across all ViewControllers
• Core Data (Best Practices)
• Using Notification Center to update ViewControllers

Watch the full course below or on the freeCodeCamp.org YouTube channel (5-hour watch).

In this tutorial for beginners, you will learn the basics of using SwiftUI to make API calls using the popular Internet Chuck Norris DataBase (ICNDB) as an example. It will display a joke quickly and easily using Swift and SwiftUI.

You'll see how the cross-platform framework SwiftUI lets us use the exact same code across iOS, iPadOS, macOS, watchOS, App Clips and tvOS, which otherwise would have been impossible.

Along with that, you will use async-await that was introduced in Swift 5.5, which works for newer operating systems including iPhones running iOS > v15.0. This really simplifies our work of making data network calls asynchronously on click of a button without freezing the UI thread.

I will share the code changes you'll need to make first. Then in the following section, I will share a brief analysis of the code so beginners can understand what's going on as well.

tvOS app running the code displays a button that retrieves the joke on click

How to Make API Calls in Swift and SwiftUI

First, you'll need a Mac to install Xcode. Once it's installed, open Xcode and create a new project. Then select "App" for iOS, macOS, tvOS, or watchOS.

ContentView

Just update your existing ContentView SwiftUI file to add a Button and use the State variable to refresh the text displayed as the joke returns from ICNDB API:

import Foundation
import SwiftUI
struct ContentView: View {
    @State private var joke: String = ""
    var body: some View {
        Text(joke)
        Button {
            Task {
                let (data, _) = try await URLSession.shared.data(from: URL(string:"https://api.chucknorris.io/jokes/random")!)
                let decodedResponse = try? JSONDecoder().decode(Joke.self, from: data)
                joke = decodedResponse?.value ?? ""
            }
        } label: {
            Text("Fetch Joke")
        }
    }
}
struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}
struct Joke: Codable {
    let value: String
}

Fetch a joke!

If you press build/play, the app will build in whatever platform you selected above:

Screenshots of watchOS, macOS, and iOS apps running the same exact code

Code Analysis

If you go to the random joke URL, you'll notice that the data is in JSON format. You can copy that and use a JSON Linter to view its structure to figure out what property of the Joke object is needed.

Based on that, you determine the code above. You use the Codable protocol (aka interfaces) to go from a JSON data object to an actual Swift class or struct, and you create properties for the data you want to store (value in our case).

JSONDecoder helps us parse the JSON string using the Codable object. This works regardless of platform because the page that loads on launching the app has the same name ContentView regardless of platform.

App Clips

App Clips are Apple's latest way of using native app functionality using an "App Clip Code" without having to download the whole application from the App Store.

App Clips work similar to an iOS app – the only difference is that you don't create a new App Clip project. You just need to add the App Clip as a target to an existing iOS app by going to File->New->Target->iOS->App Clip when an existing iOS app is open in Xcode.

If you you wondering about iPhone/iPad Widgets, well they don't animate. So button clicks will just open the corresponding app and can't update text through an external API independently.

Conclusion

In this article, you learned how to make RESTful GET API calls from SwiftUI in the simplest possible way!

Feel free to reach out to me if you have any questions. I figured this out using another article and I thought of simplifying it further. So for more details and ways to make this code more complex, check out that article:

If you're coming from Java, C++, or other object-oriented languages, chances are that you've never come across optional types or "optionals". And you might be quite surprised to know that such a concept exists in Swift.

Optionals are a fundamental topic that you need to thoroughly understand to code in Swift. If you're just getting started with Swift and you're learning about optional types for the first time, make sure to read this article until the end.

To understand what optional types are, let's quickly brush up on constants and variables.

Constants and Variables in Swift

A constant is a data item whose value, once assigned, cannot be mutated (modified or changed) throughout the scope of the program.

On the other hand, a variable is a data item whose value can be changed limitlessly.

There are some nuances in how declare constants and variables in Swift. Let's look at that syntax:

<data-item-type> <var-name>:<data-type> = <value>

Here's an example of a constant:

let pi:Double = 3.1415

And here's an example of a variable:

var message:String = "Hello, this is prajwal"
message = "Coding in swift is awesome" //variable value changed.

Notice that of the keywords we've used here for declaring constants and variables, you use let to declare a constant, and var to declare a variable.

The keyword is then followed by the constant/variable name, a colon and its data type, and then the assigning value.

Swift is a type-safety language, which means that you can assign variables and constants values without specifying the data type. It can make appropriate assumptions based on the assigned value, for example:

let const:String = "String"

can also be written as,

let const = "String"

And,

var speed:Int = 20

can be written as,

var speed = 35

You might be wondering, if you can omit the data type then what's the need to specify it anyway? Well, you're right to wonder that – but you need to specify the data type once you're working with optional types, which are different from conventional data types.

Optional types or Optionals in Swift

Coming to the main point, what are optional types in Swift?

Let's see what the docs have to say about it:

You use optionals in situations where a value may be absent. An optional represents two possibilities: Either there is a value, and you can unwrap the optional to access that value, or there isn’t a value at all.

That's a pretty straightforward definition. So optionals are basically used to handle null values at compile-time to ensure that no crashes occur at runtime.

Any operations on the optional variable are performed only if it contains non-null values.

An optional type can be of any data type, like a String, Integer, Double, Float, or any user defined non-primitive data type (object).

But, it is important to note that the Optional data type is not equivalent to its base data type. For instance, an Optional String is not the same as a string, an Optional integer is not the same as an integer, and so forth. This is because primitive data types cannot handle nil values, but Optional types can.

Optional Types Syntax and Usage in Swift

Here's the syntax for an optional type:

<data-item> <var-name>:<data-type>?

The declaration is similar to declaring regular variables, except that you add a question mark (?) beside the data type which makes it an Optional type.

Fire up your XCode playground and try running these snippets:

let someVal:Double?
someVal = 5.6324

print(someVal)
//Output : Optional(someVal)

var str:String? = nil

str = "Hello, World!"
print(str)
//Output : Optional("Hello, World!")

You can see that the outputs are not regular values. Instead, they're optional values.

How to Unwrap Optional Types in Swift

You won't use optional types upfront for any operations or tasks, as they should be cast in their primitives or user-defined instances before using it elsewhere (an optional string should be cast to a string, an optional integer should be cast to an integer, and so on).

This casting is what's known as unwrapping. You can better understand this concept by thinking about Schrödinger's cat.

In this thought experiment, a cat is placed in a closed box along with a vial of poison. Unless you open the box, you can't assure whether the cat is dead or alive ( nil or non-nil). This means that it is both dead and alive at the same time (nil and non-nil) according to your perception.

Only when you open the box (unwrapping) can you learn if the cat is alive or not (nil or not).

Unwrapping in Swift is essentially verifying if the Optional value is nil or not, and then it performs a task only if it's not nil.

You can perform unwrapping in the following ways:

1. Using an if else block
2. Using Forced unwrapping
3. Using Optional binding
4. Using Optional chaining
5. Using a nil coalescing operator

Unwrap an optional type with an if-else block

Unwrapping means to make sure that the Optional value is not nil. You can do this by using a simple if-else block like this:

var variable:String? //evaluates to nil

if variable != nil{
 print("Not nil")
}
else{
 print("Nil")
}
//Output : Nil

Unwrap an optional type with forced unwrapping

Forced unwrapping is quite contradictory because you're accessing the optional value regardless of its value (nil or not nil). If a nil optional is unwrapped, an error is thrown saying "Unexpectedly found nil while unwrapping an Optional value."

You're supposed to use forced unwrapping only in a pre-defined environment where you're certain that the optional value won't be nil.

You can forcefully unwrap an optional using the exclamatory(!) operator like this:

var color:String?;

print(color!) // Unexpectedly found nil while unwrapping an Optional value

color = "Black";

print(color!) // Black

Unwrap an optional type with optional binding

Optional binding is similar to using an if-else block. The only subtle difference is that if the optional value is not nil, the unwrapped value is assigned to a new constant and further operations are performed on the constant.

You can do this using the if-let statement:

var password:String? = "$tr0ngp@$$w0rd"

if let unwrappedpass = password {
    print("Password is \(unwrappedpass)") //Password is $tr0ngp@$$w0rd
}

An optional string password is assigned the value $tr0ngp@$$w0rd. Then in the if-let block, the optional value password is unwrapped and assigned to the variable unwrappedpass only if the optional value password is not nil. unwrappedpass now contains the unwrapped value and can be used within the block's scope.

var password:String?

if let unwrap = password{ // Block unexecuted, as optional password is nil.
    print("value is not nil")
}

Unwrap an optional type with optional chaining

You use optional chaining in places where you're dealing with multiple optional values at once. You use it to access and mutate or assign far-fetched attributes whose value depends on other constraints.

For example, we get our food from plants, which in turn get their food from sunlight and water.

This means that there is a chained dependency of events – we are dependent on plants for our food, and plants themselves are dependent on water and light for their food.

Optional chaining involves verifying at each dependency if the instance is nil or not.

Let's see how this works with a code example:

class ShipmentCar{
    var seats:Int?
    var quality:String?

    init(seatQty:Int){
        seats = seatQty
    }

    func displaySeatQuality(){
        if let seatQuality = quality{
            print("The seat covering is made of:\(seatQuality)")
        }
    }



}

class CheckSeats{
    var seatExists:ShipmentCar?

}


var obj = ShipmentCar(seatQty:4)
var obj2:CheckSeats?
obj2 = CheckSeats()
obj2?.seatExists = obj
obj2?.seatExists?.quality = "Leather" //Optional chaining, set leather quality of seats, only if seats exist.
obj.displaySeatQuality()
//Output: The seat covering is made of: Leather

In the above example, we have two classes, ShipmentCar which is cargo, and CheckSeats to check if there are any seats in the vehicle.

We first create an instance of the class ShipmentCar and pass the argument as 4 for the number of seats – meaning that there are 4 seats in the vehicle.

Further, we create an optional instance of the class CheckSeats and instantiate it. The attribute seatExists of the class CheckSeats is of the type optional ShipmentCar.

Next, we perform optional chaining on the instance obj2, which we write as obj2?.seatExists?.quality = "Leather". This means that we check if seats exist in the car, and if the seats exist, we define the quality of the seat cover which is Leather. Then we verify by calling the displaySeatQuality and get the desired result.

Here's a small caveat: in the above example, if you set the value of seatQty as 0 instead of 4, it'd still output the same result. This implies that the seat covers are made of leather even though there are 0 seats, which would make no sense.

So, I'd like to mention that this is just an example and the main objective here is to emphasize that the attributes are assigned values only if the dependent attributes are not-nil.

Unwrap an optional type with the nil coalescing operator

The nil coalescing operator works as shorthand notation for the regular if-else block. If a nil value is found when an optional value is unwrapped, an additional default value is supplied which will be used instead.

var text:String?

var output = text ?? "Default value"

print(output) // Default value

text = "This is a string"

output = text ?? "Default String"

print(output) // This is a string

You can also write default values in terms of objects.

Wrapping up

There you have it! In this article, you've learned all about optional types and how to use them.

I'd like to thank you for reading this far and I hope this article has helped you understand optional types in Swift.

If you've any queries, feel free to contact me on Twitter and/or LinkedIn. I'll be happy to help you. Cheers!

Hello, everyone! In this article we are going to learn how to add the Realm database to an iOS app.

We'll create a simple ToDo app so you can learn how to perform CRUD (Create, Read, Update, Delete) operations in the Realm database.

What is Realm?

Realm is an open-source mobile database which is developer friendly and easy to use. You can also use it as an alternative to Core Data in iOS apps.

Realm is a cross platform mobile database, which means that you can use it in native Android and iOS apps and also in cross platform apps like those created using React Native. It supports Objective-C, Swift, Java, Kotlin, C#, and JavaScript.

How to Set Up Realm in Your iOS Project

We can add Realm to our iOS project using SPM (the Swift Package Manager), Cocoa Pods, or Carthage. Here, we are going to use Cocoa Pods to add Realm Pod to our iOS project.

1. Open up Xcode and create a blank iOS app project with UIKit and Swift without using Core Data.
2. Now close Xcode and open up the terminal. Navigate to your project directory using the terminal.
3. Run the following command to create a PodFile.

pod init

4. Now when you list the contents of the directory you can see that there is a new Podfile. Open the file using any text editor (here I've used Vim). Edit your Podfile so that it looks similar to the below image. Save and close the Podfile.

Now that we have specified the dependence for Realm DB, we can install the dependencies by running the below command:

pod install

As you can see, we have successfully added the Realm DB dependency in our iOS project. Now run the below command to open our project in Xcode.

open YOUR_APP_NAME.xcworkspace

Note: after opening Xcode, make sure you build your project by pressing Command+B.

How to Design Your User Interface in Realm

We are going to keep our app's UI simple. Open up Main.storyboard and create a simple UI as shown below by adding a table view with a prototype cell. Then embed a navigation controller and create the IBOutlets for the tableview in the ViewController.swift file:

How to Create a Data Model in Realm

In our ToDo app, each task has a task name and a task id. We are going to create a Model class to represent the todo task. In the project navigator right click and create a new Swift file, and add the below code.

import Foundation
import RealmSwift


class ToDoTask:Object
{
    @objc dynamic var tasknote: String?
    @objc dynamic var taskid: String?
}

Her we created our model class named ToDoTask. It inherits the Object class which is a class that comes with RealmDB. This class handles all the under the hood processes of saving the data created using this model class in the database.

We also added two properties: tasknote, which is the task to be done, and taskid – both of type string. @objc means that your Swift code is visible to Objective C and dynamic means you want to use Objective C dynamic dispatch.

Basic CRUD App functions

Our app will perform the following functions:

1. Get input from the user using AlertViewController.
2. Add the input to the database and also to the table view.
3. Allow the user to edit their input.
4. Swipe to delete a row to remove the data from both the table view and the database.
5. Fetch all the data (if present) from the database and display it in the table view.

How to get input from the user using AlertViewController

Open up ViewController.swift and add the below code inside the ViewDidLoad() method. And create a new function called addTask() and add the code to display the alert view controller with a text box to get input from the user.

Now when the right bar button is pressed it will call the addTask() function which will display the alertviewcontroller with a text field to get user input.

navigationItem.rightBarButtonItem = UIBarButtonItem(image: .add, style: .done, target: self, action: #selector(addTask))

navigationController?.navigationBar.prefersLargeTitles = true

title = "RealmDB"

@objc
    func addTask()
    { 
        let ac = UIAlertController(title: "Add Note", message: nil, preferredStyle: .alert)

        ac.addTextField(configurationHandler: .none)

        ac.addAction(UIAlertAction(title: "Add", style: .default, handler: { (UIAlertAction) in

              if let text = ac.textFields?.first?.text
            {
                print(text)
            }

        }))
        ac.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
        present(ac, animated: true, completion: nil)
    }

How to add the input to the database and table view

To save data into Realm, first we need obtain an instance for Realm through which we can access all the methods needed for CRUD operations. Create a property of type Realm in the ViewController.swift file and initialise it in the viewDidLoad() method.

 var realmDB: Realm!

 override func viewDidLoad() {
        super.viewDidLoad()

        navigationItem.rightBarButtonItem = UIBarButtonItem(image: .add, style: .done, target: self, action: #selector(addTask))
        navigationController?.navigationBar.prefersLargeTitles = true
        title = "RealmDB"

        realmDB = try! Realm()

    }

Create an empty array of type our DataModel (ToDoTask). This array will hold all the tasks which need to be added to the table view and database.

Now inside the addTask() function modify the Add action closure so that it gets the user input and creates a random ID for that input. Then append it to our array and save it to the database.

var tasks = [ToDoTask]()

 if let text = ac.textFields?.first?.text
            {
                //Add data to data model array
                let t = ToDoTask()
                t.taskid = UUID().uuidString
                t.tasknote = text
                self.tasks.append(t)

                //Add data to database
                try! self.realmDB.write {
                    self.realmDB.add(t)
                }
                //Update table view UI
                self.tasktv.reloadData()
            }

Now when you run the app, the data will be saved in the database. But it will not show in table view because we have not implemented the delegate methods.

Make the ViewController class implement the UITableViewDelegate and UITableViewDataSource protocols and add the protocol stubs.

Now inside the numberOfRowsInSection method, return the count of our tasks array which gives the number of rows to be added to the table view. This is equal to the number of elements in tasks array.

 func tableView(_ tableView: UITableView, numberOfRowsInSection section: 
 Int) -> Int 
 {
        return tasks.count;
 }

The next thing we need to do is specify the content in each row. We can do this using the cellForRowAt delegate method. Here we dequeue a cell using the identifier which we have mentioned in storyboard and specify the label text as the tasks array element tasknote property.

 func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        if let cell = tableView.dequeueReusableCell(withIdentifier: "cell")
        {
            cell.textLabel?.text = tasks[indexPath.row].tasknote
            return cell
        }
        return UITableViewCell()
    }

How to allow users to edit their input

Now we have to allow the user to edit their entered tasks and update the changes in both the database and UI. We can do this using similar methods of getting input from the user. Implement the didSelectRowAt delegate method which will be called when user taps the table view row.

Add the below code which displays an AlertViewController with a text view. Then update the content of the cell with the entered text, and at the same time update the database contents.

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {

        let tasktomodify = tasks[indexPath.row]
        let ac = UIAlertController(title: "Update task", message: nil, preferredStyle: .alert)

        ac.addTextField(configurationHandler: .none)
        ac.addAction(UIAlertAction(title: "Ok", style: .default, handler: { (UIAlertAction) in
            if let text = ac.textFields?.first?.text
            {
                if(!text.isEmpty)
                {
                try! self.realmDB.write({
                    tasktomodify.tasknote = text
                })
                self.tasktv.reloadData()
                }
            }
        }))

        present(ac, animated: true, completion: nil)
    }

How to swipe to delete a row & remove the data from both the table view and database

Here we are going to implement a swipe to delete feature in our table view so that users can delete their tasks. But under the hood when the user swipe deletes a table view row then it should delete the data from database, data model array, and update the UI of the table view.

We can do this by implementing the commit editingStyle delegate method and adding the following code:

 func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
        if editingStyle == .delete
        {
            let tasktoDelete = tasks[indexPath.row]
            try! realmDB.write({
                realmDB.delete(tasktoDelete)
                self.tasks.remove(at: indexPath.row)
                self.tasktv.deleteRows(at: [indexPath], with: .fade)
            })
        }
    }

How to fetch all the data (if present) from the database and display it in the table view

Now we are going to implement our last operation, Read. Whenever the user launches the app, it should fetch data from the database (if data is present) and display it in the table view.

We can do this by creating a function getTodo in the view controller swift file and adding the following code inside it:

func getTodos()
    {
       //Get all the data from the database
        let notes = realmDB.objects(ToDoTask.self)

        //Clear the model data array to prevent duplicates
        self.tasks.removeAll()

        /*If the fetched data is not empty then add it to model data array and update the UI */
        if(!notes.isEmpty)
        {
        for n in notes
        {

            self.tasks.append(n)

        }
            self.tasktv.reloadData()
        }


    }

Bonus Tip: How to View Your Database Content in an iOS Simulator

Now when you run your app, you can see that it works as expected. But how can we check if the data is really stored in the database? We can use an app called MongoDB Realm Studio through which we can view our data stored in the Realm database of the simulator.

Note that this method works only when you test the app using iOS simulator

In the viewDidLoad() method, add the below line of code which will print the real file path of our app:

 print(realmDB.configuration.fileURL!)

Now copy the file path printed in the console, open up the terminal, and run the following command:

open REALM_FILE_PATH_HERE

Make sure you have downloaded MongoDB Realm Studio from the browser before running the above command.

Now it will open the RealmFile of the app in MongoDB Realm Studio. This will display the data stored in the database in a table format.

If you make changes to your data by editing or deleting the task, the changes will be reflected in the MongoDB Realm Studio app:

Congratulations! You have made a simple app which implements CRUD operations in iOS apps.

This is the second part of an article on building a Spotify UI clone with autoLayout programmatically. If you missed the first part, no worries - just please go and check it now.

In this article, we are going to add some mocked pictures and try to make the UI look the same as Spotify's.

This is what we are going to do today ?

This is were we left off in the first part:

The next step is to create customized cells. So let's start by creating one with the name SubCustomCell.

First, create a new Swift file inside the project folder and name it SubCustomCell.swift. This file will contain our custom cell that will represent the Playlist. After creating the file, try to add in the code below and initialize the cell, maybe with backgroundColor, to see the UI changes when we register the cell with the collectionView.

import UIKit

class SubCustomCell: UICollectionViewCell {
        override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = .red
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

Then we register the SubCustomCell inside CustomCell.swift within the init block. Replace UICollectionViewCell.self with SubCustomCell like below.

 collectionView.register(SubCustomCell.self, forCellWithReuseIdentifier: cellId)

Also we need to make a modification on the cellForItemAt method and make it conform to SubCustomCell like the following.

 func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! SubCustomCell
        // cell.backgroundColor = .yellow

        return cell
    }

You should see the backgroundColor changed to red .

Swift CustomCell

Up until this point everything should be straightforward and clear.

Now we're going to fill the cells with some mocked pictures and create an ImageView inside each cell. I already downloaded some random pictures from pexels.com, but feel free to use any pictures you like (including these). You can find them in the project files on Github.

Let's create the UIImageView inside SubCustomCell.swift and make some constraints.

    let ImageView : UIImageView = {
       let iv = UIImageView()
        iv.backgroundColor = .yellow
        return iv

    }()

And add it to the view within the init block using addSubView.

 override init(frame: CGRect) {
        super.init(frame: frame)
        addSubview(ImageView)

    }

Now let's make the ImageView take up all the space within the cell with the constraints below.

 ImageView.translatesAutoresizingMaskIntoConstraints = false
            ImageView.topAnchor.constraint(equalTo: topAnchor).isActive = true
            ImageView.leftAnchor.constraint(equalTo: leftAnchor).isActive = true
            ImageView.rightAnchor.constraint(equalTo: rightAnchor).isActive = true
            ImageView.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true

• LeftAnchor represents the left anchor of the cell
• rightAnchor represents the right anchor of the cell
• bottomAnchor represents the bottom anchor of the cell
• topAnchor represents the top anchor of the cell

And by making ImageView 's top anchor equal to the cell's top anchor (and doing the same for ImageView 's left, right, and bottom anchor) it makes the ImageView take up all the space of the SubCustomCell (cell).

Note: first you need to use translatesAutoresizingMaskIntoConstraints to be able to apply the constraints to the elements. Also don't forget to call isActive property and assign it to true – without doing that the constraints won't work and nothing will change.

The ImageView should have an image, so let's add one.

 let ImageView : UIImageView = {
       let iv = UIImageView()
        iv.backgroundColor = .yellow
        // we have >image1< file inside the project 
        iv.image = UIImage(named: "image1")
        iv.contentMode = .scaleAspectFill
        iv.clipsToBounds = true

        return iv

    }()

And if you build and run the app, you should see the results and picture we added to the SubCustomCell.

Cool ?. Now there is an element we should add to the SubCustomCell to finish up. We need a title that will represent the title of the playlist: UILabel.

For the title it will be like this:

 let TitleLabel : UILabel = {
        let lb = UILabel()
        lb.textColor = UIColor.lightGray
        lb.font = UIFont.systemFont(ofSize: 16)
        lb.font = UIFont.boldSystemFont(ofSize: 20)
        lb.text = "Evening Music"

        return lb
    }()

I just put some random text there – you can put whatever you like. The next step is to add the element to the view and give it some constraints. The title will be placed at the bottom of the ImageView.

Add to view:

addSubview(TitleLabel)

Applying the constraints for both the ImageView and the TitleLabel

 ImageView.translatesAutoresizingMaskIntoConstraints = false
            ImageView.topAnchor.constraint(equalTo: topAnchor).isActive = true
            ImageView.leftAnchor.constraint(equalTo: leftAnchor).isActive = true
            ImageView.rightAnchor.constraint(equalTo: rightAnchor).isActive = true
            ImageView.heightAnchor.constraint(equalToConstant: 240).isActive = true
            ImageView.bottomAnchor.constraint(equalTo: TitleLabel.topAnchor).isActive = true



            TitleLabel.translatesAutoresizingMaskIntoConstraints = false
            TitleLabel.topAnchor.constraint(equalTo: ImageView.bottomAnchor,constant: 10).isActive = true
            TitleLabel.leftAnchor.constraint(equalTo: leftAnchor, constant: 5).isActive = true
            TitleLabel.rightAnchor.constraint(equalTo: rightAnchor, constant: -5).isActive = true

And here we go!

We made the picture take up most of the space in the cell, and the rest is taken up by the title. As you can see, you can scroll horizontally in each section and also vertically in the entire screen.

Now we are put some mock data into the cells to make it feel like it's real. For that I created a JSON file that contains some random data for sections and playlists.

First let's create a two structs, Section and Playlist . We create a separate file for each struct.

section.swift

import Foundation
struct Section {
    var title : String
    var playlists : NSArray
    init(dictionary:[String : Any]) {
        self.title = dictionary["title"] as? String ?? ""
        self.playlists = dictionary["playlists"] as? NSArray ?? []

}
}

playlist.swift

//
//  playlist.swift
//  spotifyAutoLayout
//
//  Created by admin on 12/6/19.
//  Copyright © 2019 Said Hayani. All rights reserved.
//

import Foundation
struct PlayList {
    var title: String
    var image : String
    init(dictionary : [String : Any]) {
        self.title = dictionary["title"] as? String ?? ""
        self.image = dictionary["image"] as? String ?? ""
    }

}

And then inside ViewController.swift we create a function that fetches the JSON for us and stores the results in an array.

        print("attempt to fetch Json")
        if let path = Bundle.main.path(forResource: "test", ofType: "json") {
            do {
                  let data = try Data(contentsOf: URL(fileURLWithPath: path), options: .mappedIfSafe)
                  let jsonResult = try JSONSerialization.jsonObject(with: data, options: .mutableLeaves)
                if let jsonResult = jsonResult as? [ Any] {
                            // do stuff
                    jsonResult.forEach { (item) in

                        let section = Section(dictionary: item as! [String : Any])
                       // print("FEtching",section.playlists)
                        self.sections.append(section)
                    }


                  self.collectionView.reloadData()
                  }
              } catch {
                   // handle error
              }
        }
    }

The fetchJson function is called within the ViewDidLoad method. We also have a variable called sections where we store the results:

 var sections = [Section]()

The next step is to pass the data from ViewController to CustomCell. For that we create a variable inside CustomCell which will receive the data for each section:

 var section : Section?{
        didSet{
            print("section ✅",self.section)
        }
    }

We use cellForItemAt inside the ViewController method to pass the data directly to the CustomCell .

override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! CustomCell

        cell.section = sections[indexPath.item]

        return cell
    }

Note: we always call self.collectionView.reloadData() every-time fetchJson is called so the block below, inside CustomCell, will be called as well. Check the console, shift + command + C:

 var section : Section? {
        didSet{
            print("section ✅",self.section)
        }
    }

The first thing we change is to set the the section title:

 var section : Section? {
        didSet{
            print("section ✅",self.section)
            guard let section = self.section else {return}
            self.titleLabel.text = section.title
        }
    }

And then you should see that each section has a specific title on the screen ?.

Now it's time to pass the data down to SubCustomCell. We do the same thing as we did above. We need to pass the playlists array, so we create a variable named playlists inside CustomCell.

 var playlists : [PlayList]() //empty

First, we map through the playlists from the JSON. Then we add each playlist with the playlists var.

 var section : Section? {
        didSet{
            print("section ✅",self.section)
            guard let section = self.section else {return}
            self.titleLabel.text = section.title
            // append to playlists array
             self.section?.playlists.forEach({ (item) in
                let playlist = PlayList(dictionary: item as! [String : Any])
                self.playlists.append(playlist)

            })
            self.collectionView.reloadData()
        }
    }

Attention! If you try to run the app it may crash. This is because we forgot to set the number of sections. Since we are now receiving the data from JSON, the number should be dynamic based on the number of sections we have. The number of sections should be equal to the number of sections inside the JSON, so we need to modify numberOfItemsInSection inside ViewController to the below :

   override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return sections.count
    }

We do the same thing with the same method inside CustomCell.swift – but here we consider the number of the playlists instead.

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return  self.playlists.count
    }

The last step we have to complete is to pass each single playlist Object to SubCustomCell within cellForItemAt in CustomCell.swift.

 func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! SubCustomCell
        // here ?
        cell.playlist = playlists[indexPath.item]
        return cell
    }

And we are going to get that data inside SubCustomCell via the playlist variable and finally display the title and image of the playlist.

var playlist : PlayList? {
           didSet{
               print("Playlist ?",self.playlist)
            guard let playlist = self.playlist else {return}
            // The Image ?
            self.ImageView.image = UIImage(named: playlist.image)
            // the playlist title ?
            self.TitleLabel.text = self.playlist?.title

           }
       }

I think everything should work fine now, just as below ?

One last update to the UI: we have to add some padding and margins to the section and playlist titles and make the playlist a little bit smaller.

Let's first add some padding for the section titles. To do that, we need just to give the constant property some number value inside the section cell CustomCell and within setupSubCells:

 collectionView.topAnchor.constraint(equalTo: titleLabel.bottomAnchor,constant: 15).isActive = true

And if you see the entire collectionView come in at the bottom of the titleLabel, all we need to do is add more space by adding 15:

Next we come to the title of the playlist. This will be inside SubCustomCell, and we just need to add more space at the bottom of the ImageView.

 ImageView.bottomAnchor.constraint(equalTo: TitleLabel.topAnchor,constant: -15).isActive = true

We already have the constant there. In order for it to work, the value should be -15

Finally the playlist needs to be a little bit smaller. This is easy: we just make the playlist cell's height and width equal to the section cell's height divided by 2, just like below:

CustomCell.swift

 func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

        let width = frame.height / 2
        let height = frame.height / 2

        return CGSize(width: width, height: height)

    }

Make the ImageView's height equal to 150 as well.

  //SubCutomCell.swift
  ImageView.heightAnchor.constraint(equalToConstant: 150).isActive = true

And here we go ?.

Perfect! I think that's enough for today – I don't want to make this article too long. So we will have another part where we will add the TabBar and the description, as well as some icons for the playlist.

View the Full source code on GitHub?.

Thanks for your time. I hope I haven't missed anything. If I did please @mention me on Twitter, or if you have any questions or an addition to this post the doors are always open to anyone. Thanks??.

Subscribe to my email list to be notified when the third part of this tutorial is published.

By the way, I’ve recently worked with a strong group of software engineers for one of my mobile applications. The organization was great, and the product was delivered very quickly, much faster than other firms and freelancers I’ve worked with, and I think I can honestly recommend them for other projects out there. Shoot me an email if you want to get in touch — said@devsdata.com.

If you are looking to become an iOS developer, there are some fundamental skills worth knowing. First, it's important to be familiar with creating table views. Second, you should know how to populate those table views with data. Third, it's great if you can fetch data from an API and use this data in your table view.

The third point is what we'll cover in this article. Since the introduction of Codable in Swift 4, making API calls is much easier. Previously most people used pods like Alamofire and SwiftyJson (you can read about how to do that here). Now the Swift way is much nicer out of the box, so there's no reason to download a pod.

Let's go through some building blocks that are often used to make an API call. We'll cover these concepts first, as they are important parts to understanding how to make an API call.

• Completion handlers
• URLSession
• DispatchQueue
• Retain cycles

Finally we'll put it all together. I'll be using the open source Star Wars API to build this project. You can see my full project code on GitHub.

Disclaimer alert: I am new to coding and am largely self-taught. Apologies if I misrepresent some concepts.

Completion handlers

Poor patient Pheobe

Remember the episode of Friends where Pheobe is glued to the phone for days waiting to speak with customer service? Imagine if at the very start of that phone call, a lovely person called Pip said: "Thanks for calling. I have no idea how long you'll need to wait on hold, but I'll call you back when we're ready for you." It wouldn't have been as funny, but Pip is offering to be a completion handler for Pheobe.

You use a completion handler in a function when you know that function will take a while to complete. You don't know how long, and you don't want to pause your life waiting for it to finish. So you ask Pip to tap you on the shoulder when she's ready to give you the answer. That way you can go about your life, run some errands, read a book, and watch TV. When Pip taps on you on the shoulder with the answer, you can take her answer and use it.

This is what happens with API calls. You send a URL request to a server, asking it for some data. You hope the server returns the data quickly, but you don't know how long it will take. Instead of making your user wait patiently for the server to give you the data, you use a completion handler. This means you can tell your app to go off and do other things, such as loading the rest of the page.

You tell the completion handler to tap your app on the shoulder once it has the information you want. You can specify what that information is. That way, when your app gets tapped on the shoulder, it can take the information from the completion handler and do something with it. Usually what you'll do is reload the table view so the data appears to the user.

Here's an example of what a completion handler looks like. The first example is setting up the API call itself:

func fetchFilms(completionHandler: @escaping ([Film]) -> Void) {
  // Setup the variable lotsOfFilms
  var lotsOfFilms: [Film]

  // Call the API with some code

  // Using data from the API, assign a value to lotsOfFilms  

  // Give the completion handler the variable, lotsOfFilms
  completionHandler(lotsOfFilms)
}

Now we want to call the function fetchFilms. Some things to note:

• You don't need to reference completionHandler when you call the function. The only time you reference completionHandler is inside the function declaration.
• The completion handler will give us back some data to use. Based on the function we've written above, we know to expect data which is of type [Film]. We need to name the data so that we can refer to it. Below I'm using the name films, but it could be randomData, or any other variable name I'd like.

The code will look something like this:

fetchFilms() { (films) in
  // Do something with the data the completion handler returns 
  print(films)
}

URLSession

URLSession is like the manager of a team. The manager doesn't do anything on her own. Her job is to share the work with the people in her team, and they'll get the job done. Her team are dataTasks. Every time you need some data, write to the boss and use URLSession.shared.dataTask.

You can give the dataTask different types of information to help you achieve your goal. Giving information to dataTask is called initialization. I initialism my dataTasks with URLs. dataTasks also use completion handlers as part of their initialization. Here's an example:

let url = URL(string: "https://www.swapi.co/api/films")

let task = URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in 
  // your code here
})

task.resume()

dataTasks use completion handlers, and they always return the same types of information: data, response and error. You can give these data types different names, like (data, res, err) or (someData, someResponse, someError). For the sake of convention, it's best to stick to something obvious rather than go rogue with new variable names.

Let's start with error. If the dataTask returns an error, you'll want to know that upfront. It means you can direct your code to handle the error gracefully. It also means you won't bother trying to read the data and do something with it as there is an error in returning the data.

Below I am handling the error really simply by printing an error to the console and exiting the function. There are many other ways you could handle the error if you wanted to. Think about how fundamental this data is to your app. For example, if you have a banking app and this API call shows users their balance, then you may want to handle the error by presenting a modal to the user that says, "Sorry, we're experiencing a problem right now. Please try again later."

if let error = error {
  print("Error accessing swapi.co: /(error)")
  return
}

Next we look at the response. You can cast the response to be an httpResponse. That way you can look at the status codes and make some decisions based on the code. For example, if the status code is 404, then you know the page was not found.

The code below uses a guard to check that two things exist. If both exist, then it allows the code to continue to the next statement after the guard clause. If either of the statements fail, then we exit the function. This is a typical use case of a guard clause. You expect the code after a guard clause to be the happy days flow (i.e. the easy flow with no errors).

  guard let httpResponse = response as? HTTPURLResponse,
            (200...299).contains(httpResponse.statusCode) else {
    print("Error with the response, unexpected status code: \(response)")
    return
  }

Finally you handle the data itself. Notice that we haven't used the completion handler for the error or the response. That's because the completion handler is waiting for data from the API. If it doesn't get to the data part of the code, there's no need to invoke the handler.

For the data, we are using the JSONDecoder to parse the data in a nice way. This is pretty nifty, but requires that you have established a model. Our model is called FilmSummary. If JSONDecoder is new to you, then have a look online for how to use it and how to use Codable. It's really simple in Swift 4 and above compared to the Swift 3 days.

In the code below, we are first checking that the data exists. We are pretty sure it should exist, because there are no errors and no strange HTTP responses. Second, we check that we can parse the data we receive in the way we expect. If we can, then we return the film summary to the completion handler. Just in case there is no data to return from the API, we have a fall back plan of the empty array.

if let data = data,
        let filmSummary = try? JSONDecoder().decode(FilmSummary.self, from: data) {
        completionHandler(filmSummary.results ?? [])
      }

So the full code for API call looks like this:

func fetchFilms(completionHandler: @escaping ([Film]) -> Void) {
    let url = URL(string: domainUrlString + "films/")!

    let task = URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
      if let error = error {
        print("Error with fetching films: \(error)")
        return
      }

      guard let httpResponse = response as? HTTPURLResponse,
            (200...299).contains(httpResponse.statusCode) else {
        print("Error with the response, unexpected status code: \(response)")
        return
      }

      if let data = data,
        let filmSummary = try? JSONDecoder().decode(FilmSummary.self, from: data) {
        completionHandler(filmSummary.results ?? [])
      }
    })
    task.resume()
  }

Retain cycles

NB: I am extremely new to understanding retain cycles! Here's the gist of what I researched online.

Retain cycles are important to understand for memory management. Basically you want your app to clean up bits of memory that it doesn't need anymore. I assume this makes the app more performant.

There are lots of ways that Swift helps you do this automatically. However there are many ways that you can accidentally code retain cycles into your app. A retain cycle means that your app will always hold on to the memory for a certain piece of code. Generally it happens when you have two things that have strong pointers to each other.

To get around this, people often use weak. When one side of the code is weak, you don't have a retain cycle and your app will be able to release the memory.

For our purpose, a common pattern is to use [weak self] when calling the API. This ensures that once the completion handler returns some code, the app can release the memory.

fetchFilms { [weak self] (films) in
  // code in here
}

DispatchQueue

Xcode uses different threads to execute code in parallel. The advantage of multiple threads means you aren't stuck waiting on one thing to finish before you can move on to the next. Hopefully you can start to see the links to completion handlers here.

These threads seem to be also called dispatch queues. API calls are handled on one queue, typically a queue in the background. Once you have the data from your API call, most likely you'll want to show that data to the user. That means you'll want to refresh your table view.

Table views are part of the UI, and all UI manipulations should be done in the main dispatch queue. This means somewhere in your view controller file, usually as part of the viewDidLoad function, you should have a bit of code that tells your table view to refresh.

We only want the table view to refresh once it has some new data from the API. This means we'll use a completion handler to tap us on the shoulder and tell us when that API call is finished. We'll wait until that tap before we refresh the table.

The code will look something like:

fetchFilms { [weak self] (films) in
  self.films = films

  // Reload the table view using the main dispatch queue
  DispatchQueue.main.async {
    tableView.reloadData()
  }
}

viewDidLoad vs viewDidAppear

Finally you need to decide where to call your fetchfilms function. It will be inside a view controller that will use the data from the API. There are two obvious places you could make this API call. One is inside viewDidLoad and the other is inside viewDidAppear.

These are two different states for your app. My understanding is viewDidLoad is called the first time you load up that view in the foreground. viewDidAppear is called every time you come back to that view, for example when you press the back button to come back to the view.

If you expect your data to change in between the times that the user will navigate to and from that view, then you may want to put your API call in viewDidAppear. However I think for almost all apps, viewDidLoad is sufficient. Apple recommends viewDidAppear for all API calls, but that seems like overkill. I imagine it would make your app less performant as it's making many more API calls that it needs to.

Combining all the steps

First: write the function that calls the API. Above, this is fetchFilms. This will have a completion handler, which will return the data you are interested in. In my example, the completion handler returns an array of films.

Second: call this function in your view controller. You do this here because you want to update the view based on the data from the API. In my example, I am refreshing a table view once the API returns the data.

Third: decide where in your view controller you would like to call the function. In my example, I call it in viewDidLoad.

Fourth: decide what to do with the data from the API. In my example, I am refreshing a table view.

Inside NetworkManager.swift (this function can be defined in your view controller if you'd like, but I am using the MVVM pattern).

func fetchFilms(completionHandler: @escaping ([Film]) -> Void) {
    let url = URL(string: domainUrlString + "films/")!

    let task = URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
      if let error = error {
        print("Error with fetching films: \(error)")
        return
      }

      guard let httpResponse = response as? HTTPURLResponse,
            (200...299).contains(httpResponse.statusCode) else {
        print("Error with the response, unexpected status code: \(response)")
        return
      }

      if let data = data,
        let filmSummary = try? JSONDecoder().decode(FilmSummary.self, from: data) {
        completionHandler(filmSummary.results ?? [])
      }
    })
    task.resume()
  }

Inside FilmsViewController.swift:

final class FilmsViewController: UIViewController {
  private var films: [Film]?

  override func viewDidLoad() {
    super.viewDidLoad()

    NetworkManager().fetchFilms { [weak self] (films) in
      self?.films = films
      DispatchQueue.main.async {
        self?.tableView.reloadData()
      }
    }
  }

  // other code for the view controller
}

Gosh, we made it! Thanks for sticking with me.

In this post we will try to re-create the Spotify home screen layout in Swift programmatically. Why programmatically? I think it's always good to know how to build things in different ways, and I like to write code to do things programmatically. These skills are especially helpful if you are working with team or using version control.

This is the actual home screen of Spotify's mobile app. So to achieve this kind of layout, we will be using UICollectionView, and we may use TabBarController as well to create the tab navigator.

Basic requirement : First make sure you have Xcode +10 installed and swift +4.

Let's start by creating a new Xcode project using Xcode:

And the first thing we need to do in ViewController.swift is change the superClass to UICollectionViewController instead of UIViewController because our class will be based on collectionView.

//
//  ViewController.swift
//  spotifyAutoLayout
//
//  Created by admin on 10/31/19.
//  Copyright © 2019 Said Hayani. All rights reserved.
//

import UIKit

class ViewController: UICollectionViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        collectionView.backgroundColor = .purple
        // Do any additional setup after loading the view.
    }


}

If you try to run the app the build will fail. We need to add some code to the AppDelegate.swift file within the didFinishLaunchingWithOptions function past this piece of code before the return statement:

  let layout = UICollectionViewFlowLayout()
        window = UIWindow()
        window?.rootViewController = ViewController(collectionViewLayout: layout)

And the code should look like this:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        let layout = UICollectionViewFlowLayout()
        window = UIWindow()
        window?.rootViewController = ViewController(collectionViewLayout: layout)
        return true
    }

Now you should be able to run the app and see the backgroundColor changed to purple:

The next step is to distribute the layout and divide the space equally between the sections.

Let's define the methods of our CollectionView.

The steps:

• Register a reusable cell with unique identifier
• Define the number of the items in the section
• Use the the registered cell

To use some of CollectionView methods we need to always conform to UICollectionViewDelegateFlowLayout as a superClass and to get the autoComplete of the methods. So let's start with registering the CollectionViewCell.

Inside View.DidLoad() we call the collectionView.register() method to register the reusable cell:

  collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: cellId)

Then we define the number of cells we will have inside the collectionView using numberOfItemsInSection. For now we just need to make it 5 items:

 override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 5
    }

The next step is to define the reusable cell using cellForItemAt that should return UICollectionViewCell and have a unique id called cellId. The code looks like this:

 override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath)
        cell.backgroundColor = .red
        return cell
    }

The full code should look like this:

import UIKit

class ViewController: UICollectionViewController, UICollectionViewDelegateFlowLayout {
    let cellId : String = "cellId"

    override func viewDidLoad() {
        super.viewDidLoad()
        collectionView.backgroundColor = .purple
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: cellId)

    }


    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 5
    }
    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath)
        cell.backgroundColor = .red
        return cell
    }

}

You should be able to see 5 items with red backgrounds on the screen:

Add a custom width and height to the cells

Now we need to place the cells in the correct order and give them a width and height. Each cell will take the width of the screen as width.

We are lucky to have sizeForItemAt method so we can give the cells a custom width and height. It's a method that should return a CGSize type:

 func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let width = view.frame.width
        let height = CGFloat(200)

        return CGSize(width: width, height: height)
    }

So we made the Cell take the width of the screen by using view.frame.width and a custom height with is a CGFloat type.

Now you can see the result below in your Simulator :

Everything looks good so far. This time let's create a custom cell that can be reusable. Create a new Swift file named CustomCell:

CustomCell.swift should look like this below:

import UIKit

class CustomCell: UICollectionViewCell {
    override init(frame: CGRect) {
        super.init(frame: frame)

    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

Now the next things we have to do is to modify two methods to support the reusable cell, collectionView.register and cellForItemAt. Let's first modify the register method. Replace UICollectionViewCell.**self** with CustomCell:

 collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: cellId)

Next we need to cast cellForItemAt to conform to CustomCell like below:

  let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! CustomCell

If you run the app probably you won't notice any change, so give the CustomCell a backgroundColor backgroundColor = .yellow. Don't forget to remove the line cell.backgroundColor = .red in cellForItemAt. You should see the background color changed to yellow ?

Now it's time to put some salt into CutomCell :D

If you look at the Spotify home screen, each section which is a CustomCell in our example contains a section title, sub cells, and is horizontal:

Add a section title

Let's add a title label to the cell. Create the titleLabel element inside the CutomCell class:

let titleLabel: UILabel = {
        let lb  = UILabel()
        lb.text = "Section Title"
        lb.font = UIFont.boldSystemFont(ofSize: 14)
        lb.font = UIFont.boldSystemFont(ofSize: 14)

        return lb
    }()

Then add the element to the view inside init() block:

addSubview(titleLabel)

If you run the app you won't see any changes, and that's because we didn't put any constraint to the element yet. So let's add some constraints – add this property lb.translatesAutoresizingMaskIntoConstraints = **false** to titleLabel to be able to apply constraints to the element:

After we add titleLabel to the view, we define the constraints:

 addSubview(titleLabel)
titleLabel.topAnchor.constraint(equalTo: topAnchor, constant: 8).isActive = truetitleLabel.leftAnchor.constraint(equalTo: leftAnchor,constant: 8 ).isActive = true

Always make sure to add .isActive = true property – without it the constraint won't work!

Before we move on to the next part, let's first change the background color of the screen to black and also remove the yellow color for the cells:

Now comes the big part: putting sub cells into each cell. To achieve that we are going to add a CollectionView inside CustomCell.

To add a CollectionView inside UICollectionViewCell we need to add properties UICollectionViewDelegate, UICollectionViewDelegateFlowLayout, and UICollectionViewDataSource as superClass to CustomCell.

Let's create the collectionView element as any simple view:

    let collectionView : UICollectionView = {
        // init the layout
        let layout = UICollectionViewFlowLayout()
        // set the direction to be horizontal
        layout.scrollDirection = .horizontal

        // the instance of collectionView

        let cv = UICollectionView(frame: .zero, collectionViewLayout: layout)

        // Activate constaints

        cv.translatesAutoresizingMaskIntoConstraints = false

        return cv

    }()

Notice that we add layout to the collectionView as layer in the initializer as we did the first time with the viewController.swift. Here we also specify the direction of the FlowLayout to be .horizontal.

Let's add the collectionView element to the view as subView.

We gonna make a function that do that for us to make the code a little bit cleaner.

    fileprivate  func setupSubCells(){
        // add collectionView to the view
        addSubview(collectionView)

        collectionView.dataSource = self
        collectionView.delegate = self
        // setup constrainst
        // make it fit all the space of the CustomCell
        collectionView.topAnchor.constraint(equalTo: titleLabel.bottomAnchor).isActive = true
        collectionView.leftAnchor.constraint(equalTo: leftAnchor).isActive = true
        collectionView.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
        collectionView.rightAnchor.constraint(equalTo: rightAnchor).isActive = true
    }

Make sure to set delegate to self for the collectionView and the dataSource as well:

collectionView.dataSource = self

collectionView.delegate = self

Then call the function within init block.

Xcode will display some errors if you trying to build the app because we are not conforming to UICollectionViewDelegate and UICollectionViewDelegateFlowLayout protocols. To fix that we need first to register the sub cell as a reusable cell.

Create a variable at the top of the class and give it a name of cellId so we can use it when we need the cell identifier:

let cellId : String = "subCellID"

collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: cellId)

Now we're missing two more methods to make the errors go away: numberOfItemsInSection that define the number of cells in the section and cellForItemAt that define the reusable cell. These methods are necessary for collectionView to work properly:

 // number of cells
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
       return  4
    }

    // reusable Cell
     func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath)
         cell.backgroundColor = .yellow

        return cell
    }

The results should look like this:

As you can see, the collectionView are in purple as background and sub cells are yellow.

The last things we can do before ending this article is make subCells have the height of the section and as width. Again we are using sizeForItemAt to define the height and the width of the cell .

 func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

        let width = frame.height
        let height = frame.height

        return CGSize(width: width, height: height)

    }

And here we are ?:

NICE! I'm gonna stop at this point so this post isn't too long. I'll make a second part where we are going to add some mocked pictures and fill it with some data.

Full source code ? here

Please please if you have any additions, questions, or corrections, post it in the comments below ? or hit me up on Twitter.

Subscribe to my email list to be notified when the second part of this tutorial is published

Building a design system to support one product is not easy - it has to be robust and flexible at the same time for scalability. Though challenging, lots of great resources have shared useful principles and approaches that help teams build a good system both visually and programmatically. Standing on their shoulders, this article tries to contribute to an untouched ground by focusing on building a good system in SwiftUI.

Why do I write this article

During my first summer in ITP at New York, I'm lucky to have the opportunity to work as an iOS developer intern at Line Break Studio. One task I've been assigned to is building a design system in two steps: first visually in Sketch, and then programmatically in SwiftUI. The experience of experimenting with the new framework and building a design system with it has been amazing, but also buggy along the way. That's why we'd like to share our experience with the community, hopefully making your development process easier.

What is SwiftUI

Apple released this groundbreaking new framework in WWDC 2019, which is one of the bests in years. From the point of view as a web developer, the project development experience in SwiftUI is closer to which in conventional front-end stack and frameworks.

This is definitely an awesome move because programming interface and managing states are drastically easier than before. And the best part of this improvement is that one can integrate UIKit and SwiftUI smoothly. To learn the basics of SwiftUI, the official tutorials provided by Apple are very helpful.

The demo project

For demonstration purpose, I put up a simplified version of design system we built in Line Break Studio. It a set of button components in different forms, which are built on top of two lower level parts: typography and colorPalette.

Dynamic rendering view of the demo project

The project is public on GitHub, and I'm using Xcode 11 Beta 5 for development. An Airtable base as design system management hub (read more about workflow management) is also public for reference.

Principles of building design system

Design system in code is a middleware between designers and developers. Developer of the system takes inputs from design system in visual form, and produces API that's identical with which for further development. Following two principles should be recognized to complete this system in code:

1. Communicate with tokens

Fundamentally, the purpose of having a design system in program is not about better code management or development efficiency, but to make sure the view is consistent with design files. To achieve that goal, using tokens to signify certain color, font, size or any visual elements is crucial to maintain quality of communication between developers, designers and managers in a team.

Lightning Design System's tokens built by Salesforce

2. Levels of hierarchy

In EightShapes' article, it points out that we should "Show options first, then decisions next", because "You can't make decisions without options."

EightShapes' article about design tokens

This kind of ordering architecture loosens the degree of coupling between different levels, hence providing more flexibility and dynamic for possible revisions. The way I structure the levels is in this order from bottom to top: material → base → token. But it could be anyway the team's comfortable with.

Diving into code

Following section is a list of highlights we'd like to point out based on our experience. Please visit the GitHub repo for complete code. Any feedbacks or critics are welcome for improvements.

1. Architecting levels of hierarchy

There're two ways of stacking materials at lower level to construct tokens at highest level:

• Use enum for type safety and code literacy

Advantages of using enum in code as grouping wrapper or parameter in function have already been well recognized. One point worths mentioning here is the implementation of levels of hierarchy.

We always store the raw values, including font size (CGFloat) and font name (String), at the lowest level, because we don't want to mess around with it. But because raw value must be a literal in enum, we can't just assign a case to be a value from the other enum.

To work around this problem, we implement a function getValue, which returns the raw value in switch case when necessary.

• Use struct for easier structure

Though enum is great, we don't need its unique feature in some cases. For example, because Xcode takes care of the heavy job of processing dynamic colors, and no parameter options are required in API endpoint, we can set up color palettes by simple two levels of struct.

2. Clear and straightforward naming of API endpoint

Naming convention is another broad topic for discussion and debate. In addition to basic Swift conventions, the only two rules we abide are, 1) no acronym and 2) making it simple. For example, to use typography and color system, instead of creating new endpoints, we make extension from Font and Color structs. This approach decreases the effort to memorize unfamiliar API names for developers.

3. Manage color sets dynamically in two modes

So dark mode has become a standard in industry, and both iOS and Android team have implemented this feature. It's a good trend for users, but could bring designers and developers some challenges, including managing and naming the color sets, especially gray scale ones.

Material Design's dark theme guide

To think and communicate about gray scale colors dynamically, using terms like white, light, black or dark doesn't work. Because if we referred to a dynamic color #000000 (black in HEX) black or dark in light color scheme, how do you talk about this particular color, which should turn into #FFFFFF (white in HEX), in dark color scheme? defaultDark or lightDark?

Confusing transition of color sets

It is very confusing to name gray scale dynamic color sets in conventional approach. To avoid this confusion, we use theme and contrast to manage one set of color in light and dark schemes instead.

Example color naming in demo Airtable base

Note that a gray scale color doesn't always need to be reversed in opposite color mode. In these situations that light color remains light and dark remains dark, we simply name name it light or dark instead.

Once we wrap our head around this naming method, managing this architecture of color palette is easy in Xcode. To create a color set, simply create a new Asset Catalog file → add a new Color Set → and change Appearances to Any, Light, Dark will do.

How to add color asset in Xcode

4. environment settings

One awesome feature in SwiftUI framework is the environment modifier, which provides ability to control environment values on target view. In terms of building design system, this ability provides convenient approach to change app's font at root level. And the other advantage of using environmentValue is to change and test light and dark color schemes in development.

5. buttonStyle and button label

Comparing to the old days in UIKit, constructing reusable buttons in SwiftUI is drastically easier. The Button view consists of two parts, which are action closure (event to be fired as button is pressed) and label (body of the button). The view can then be chained with a modifier buttonStyle. To learn details about building reusable buttons,I recommend reading Alejandro's tutorial, which is comprehensive and useful.

In our customized button components, first step is to create two structs, including TokenButtonLabel and TokenButtonStyle. These two structs are programmed according to the types of buttons we have in design files. For example, there're only two types of labels: icon and text. Each type has an according init function designed with different parameters for new instances.

On the other hand, there're four major types of button styles: circle icon, icon, capsule and text. To follow ButtonStyle protocol, a makeBody func has to be implemented. This function brings us a configuration property, providing a native isPressed value to monitor if the button is pressed or not.

Finally, stacking on top of TokenButtonLabel and TokenButtonStyle, the endpoint of the button component API will be TokenButton - a grouping that wraps content and style of button together, conforming to the button types in visual design system.

6. AnyView as wrapper

As we're dealing with the makeBody function brought by ButtonStyle protocol, we found a useful tip to work with View. To store a view in a variable, the type annotation could be indicated as AnyView, which works as a general container of views in SwiftUI.

In our case, because we want to add the opacity modifier to configuration.label to all types of buttons, instead of doing so repeatedly in each switch case, it makes more sense to chain the modifier at the end altogether. We can achieve this pattern by using the advantage of AnyView in this way:

7. Build view modifier with mutating function

To update styles of the buttons dynamically, we can build our own modifier. First instantiate customized mutable state properties in view, and then create a mutating function which returns a Self type after updating the target state property.

8. Tricky border style

One drawback of SwiftUI is styling a circle shape with circular border is not straightforward at all. I struggled for a while, and finally found a solution here on StackOverflow. A clipShape and an overlay modifier are required to make it work.

Conclusion

SwiftUI is an incredible improvement Apple makes. Though flaws still exist, building a robust and flexible design system with it, and furthermore complicated UI in iOS is way efficient than ever. I hope this article is helpful for any iOS team trying to build UI, and always welcome to any feedbacks!

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