Tutorial 17: Multithreading with Grand Central Dispatch (GCD) and Async/Await in Swift

Introduction Multithreading is a key technique in iOS development for ensuring smooth user experiences. Swift provides two powerful tools for managing concurrent tasks: Grand Central Dispatch (GCD) and Async/Await. GCD is a low-level API for managing background tasks efficiently. Async/Await is a modern Swift concurrency feature that simplifies asynchronous programming with structured concurrency. In this tutorial, we will learn how to use these concepts by building a Voice Recorder app that runs in the background. Section 1: Understanding GCD and Async/Await What is Grand Central Dispatch (GCD)? GCD is Apple's technology for managing threads and task execution asynchronously. It provides: Dispatch Queues (Serial & Concurrent) Main and Background Queues Work Items (sync vs async execution) Example: Running tasks with GCD DispatchQueue.global(qos: .background).async { print("This is running in the background") } What is Async/Await? Async/Await simplifies writing asynchronous code. It allows developers to work with concurrency in a more readable manner. Example: Using Async/Await in Swift func fetchData() async throws -> String { let result = try await someAsyncFunction() return result } Section 2: Setting Up the Voice Recorder App Creating the Xcode Project Open Xcode and create a new iOS project. Select App, choose SwiftUI as the interface, and name it "VoiceRecorder". Enable background mode for Audio in the project settings. Section 3: Implementing Audio Recording with AVAudioRecorder Import AVFoundation import AVFoundation Request Microphone Permissions class AudioRecorder: NSObject, ObservableObject { private var audioRecorder: AVAudioRecorder? private var recordingSession: AVAudioSession = AVAudioSession.sharedInstance() override init() { super.init() requestPermissions() } private func requestPermissions() { recordingSession.requestRecordPermission { allowed in DispatchQueue.main.async { if allowed { print("Microphone access granted") } else { print("Microphone access denied") } } } } } Section 4: Recording and Saving Audio Start and Stop Recording func startRecording() { let audioFilename = getDocumentsDirectory().appendingPathComponent("recording.m4a") let settings = [ AVFormatIDKey: Int(kAudioFormatMPEG4AAC), AVSampleRateKey: 12000, AVNumberOfChannelsKey: 1, AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue ] do { audioRecorder = try AVAudioRecorder(url: audioFilename, settings: settings) audioRecorder?.record() print("Recording started") } catch { print("Recording failed: \(error.localizedDescription)") } } func stopRecording() { audioRecorder?.stop() print("Recording stopped") } Helper Function to Get Directory func getDocumentsDirectory() -> URL { FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0] } Section 5: Running Tasks in the Background Enable Background Audio Open Signing & Capabilities. Add Background Modes and enable Audio, AirPlay, and Picture in Picture. Keep the Recording Running in the Background func configureAudioSession() { do { try recordingSession.setCategory(.playAndRecord, mode: .default, options: .defaultToSpeaker) try recordingSession.setActive(true) } catch { print("Failed to configure audio session: \(error.localizedDescription)") } } Section 6: Integrating Async/Await for Smooth UI Using Async/Await for File Saving func saveRecording() async { let audioFile = getDocumentsDirectory().appendingPathComponent("recording.m4a") do { try await Task.sleep(nanoseconds: 2_000_000_000) // Simulate background work print("File saved at: \(audioFile)") } catch { print("Error saving file: \(error.localizedDescription)") } } Handling UI Updates in the Main Thread DispatchQueue.main.async { self.isRecording = false } Section 7: Building the SwiftUI Interface Designing the UI import SwiftUI struct ContentView: View { @StateObject private var audioRecorder = AudioRecorder() var body: some View { VStack { Button(action: { audioRecorder.startRecording() }) { Text("Start Recording") .padding() .background(Color.red) .foregroundColor(.white) .clipShape(Capsule()) } Button(action: {

DispatchQueue.global(qos: .background).async {
    print("This is running in the background")
}

func fetchData() async throws -> String {
    let result = try await someAsyncFunction()
    return result
}

import AVFoundation

class AudioRecorder: NSObject, ObservableObject {
    private var audioRecorder: AVAudioRecorder?
    private var recordingSession: AVAudioSession = AVAudioSession.sharedInstance()

    override init() {
        super.init()
        requestPermissions()
    }

    private func requestPermissions() {
        recordingSession.requestRecordPermission { allowed in
            DispatchQueue.main.async {
                if allowed {
                    print("Microphone access granted")
                } else {
                    print("Microphone access denied")
                }
            }
        }
    }
}

func startRecording() {
    let audioFilename = getDocumentsDirectory().appendingPathComponent("recording.m4a")

    let settings = [
        AVFormatIDKey: Int(kAudioFormatMPEG4AAC),
        AVSampleRateKey: 12000,
        AVNumberOfChannelsKey: 1,
        AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue
    ]

    do {
        audioRecorder = try AVAudioRecorder(url: audioFilename, settings: settings)
        audioRecorder?.record()
        print("Recording started")
    } catch {
        print("Recording failed: \(error.localizedDescription)")
    }
}

func stopRecording() {
    audioRecorder?.stop()
    print("Recording stopped")
}

func getDocumentsDirectory() -> URL {
    FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
}

func configureAudioSession() {
    do {
        try recordingSession.setCategory(.playAndRecord, mode: .default, options: .defaultToSpeaker)
        try recordingSession.setActive(true)
    } catch {
        print("Failed to configure audio session: \(error.localizedDescription)")
    }
}

func saveRecording() async {
    let audioFile = getDocumentsDirectory().appendingPathComponent("recording.m4a")

    do {
        try await Task.sleep(nanoseconds: 2_000_000_000) // Simulate background work
        print("File saved at: \(audioFile)")
    } catch {
        print("Error saving file: \(error.localizedDescription)")
    }
}

DispatchQueue.main.async {
    self.isRecording = false
}

import SwiftUI

struct ContentView: View {
    @StateObject private var audioRecorder = AudioRecorder()

    var body: some View {
        VStack {
            Button(action: {
                audioRecorder.startRecording()
            }) {
                Text("Start Recording")
                    .padding()
                    .background(Color.red)
                    .foregroundColor(.white)
                    .clipShape(Capsule())
            }

            Button(action: {
                audioRecorder.stopRecording()
            }) {
                Text("Stop Recording")
                    .padding()
                    .background(Color.blue)
                    .foregroundColor(.white)
                    .clipShape(Capsule())
            }
        }
    }
}

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