Background Modes詳細解析（二） —— 幾種Mode使用示例（二） 版本記錄 前言 源碼 後記

版本記錄

版本號	時間
V1.0	2022.11.06 星期日

前言

Background Modes我們在程序中總會用到，包括語音、定位更新、後臺任務以及遠程通知等，這個模塊我們就一起來學習下。感興趣的可以看下面幾篇文章。
1. Background Modes詳細解析（一） —— 幾種Mode使用示例（一）

源碼

1. Swift

首先看下工程組織架構

下面就是源碼了

1. AppMain.swift

import SwiftUI

@main
struct AppMain: App {
  @UIApplicationDelegateAdaptor(AppDelegate.self) var appDelegate

  var body: some Scene {
    WindowGroup {
      ContentView()
    }
  }
}

2. AppDelegate.swift

import UIKit
import BackgroundTasks

class AppDelegate: UIResponder, UIApplicationDelegate {
  static var dateFormatter: DateFormatter = {
    let formatter = DateFormatter()
    formatter.dateStyle = .short
    formatter.timeStyle = .long
    return formatter
  }()

  var window: UIWindow?

  func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil
  ) -> Bool {
    BGTaskScheduler.shared.register(
      forTaskWithIdentifier: AppConstants.backgroundTaskIdentifier,
      using: nil) { task in
        self.refresh()
        task.setTaskCompleted(success: true)
        self.scheduleAppRefresh()
    }

    scheduleAppRefresh()
    return true
  }

  func scheduleAppRefresh() {
    let request = BGAppRefreshTaskRequest(identifier: AppConstants.backgroundTaskIdentifier)
    request.earliestBeginDate = Date(timeIntervalSinceNow: 1 * 60)
    do {
      try BGTaskScheduler.shared.submit(request)
      print("background refresh scheduled")
    } catch {
      print("Couldn't schedule app refresh \(error.localizedDescription)")
    }
  }

  func refresh() {
    // to simulate a refresh, just update the last refresh date to current date/time
    let formattedDate = Self.dateFormatter.string(from: Date())
    UserDefaults.standard.set(formattedDate, forKey: UserDefaultsKeys.lastRefreshDateKey)
    print("refresh occurred")
  }
}

3. AppConstants.swift

import Foundation

enum AppConstants {
  static let backgroundTaskIdentifier = "com.mycompany.myapp.task.refresh"
}

enum UserDefaultsKeys {
  static let lastRefreshDateKey = "lastRefreshDate"
}

4. AudioModel.swift

import SwiftUI
import AVFoundation
import Combine

extension AudioView {
  class Model: ObservableObject {
    @Published var time: TimeInterval = 0
    @Published var item: AVPlayerItem?
    @Published var isPlaying = false

    var itemTitle: String {
      if let asset = item?.asset as? AVURLAsset {
        return asset.url.lastPathComponent
      } else {
        return "-"
      }
    }

    private var itemObserver: AnyCancellable?
    private var timeObserver: Any?
    private let player: AVQueuePlayer

    init() {
      do {
        try AVAudioSession
          .sharedInstance()
          .setCategory(.playback, mode: .default)
      } catch {
        print("Failed to set audio session category. Error: \(error)")
      }

      self.player = AVQueuePlayer(items: Self.songs)
      player.actionAtItemEnd = .advance

      itemObserver = player.publisher(for: \.currentItem).sink { [weak self] newItem in
        self?.item = newItem
      }

      timeObserver = player.addPeriodicTimeObserver(
        forInterval: CMTime(seconds: 0.5, preferredTimescale: 600),
        queue: nil) { [weak self] time in
          self?.time = time.seconds
      }
    }

    func playPauseAudio() {
      isPlaying.toggle()
      if isPlaying {
        player.play()
      } else {
        player.pause()
      }
    }

    static var songs: [AVPlayerItem] = {
      // find the mp3 song files in the bundle and return player item for each
      let songNames = ["FeelinGood", "IronBacon", "WhatYouWant"]
      return songNames.map {
        guard let url = Bundle.main.url(forResource: $0, withExtension: "mp3") else {
          return nil
        }
        return AVPlayerItem(url: url)
      }
      .compactMap { $0 }
    }()
  }
}

5. LocationModel.swift

import Combine
import CoreLocation
import MapKit

extension LocationView {
  class Model: NSObject, CLLocationManagerDelegate, ObservableObject {
    @Published var isLocationTrackingEnabled = false
    @Published var location: CLLocation?
    @Published var region = MKCoordinateRegion(
      center: CLLocationCoordinate2D(latitude: 51.507222, longitude: -0.1275),
      span: MKCoordinateSpan(latitudeDelta: 0.5, longitudeDelta: 0.5))
    @Published var pins: [PinLocation] = []

    let mgr: CLLocationManager

    override init() {
      mgr = CLLocationManager()
      mgr.desiredAccuracy = kCLLocationAccuracyBest
      mgr.requestAlwaysAuthorization()
      mgr.allowsBackgroundLocationUpdates = true

      super.init()
      mgr.delegate = self
    }

    func enable() {
      mgr.startUpdatingLocation()
    }

    func disable() {
      mgr.stopUpdatingLocation()
    }

    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
      if let currentLocation = locations.first {
        print(currentLocation)
        location = currentLocation
        appendPin(location: currentLocation)
        updateRegion(location: currentLocation)
      }
    }

    func appendPin(location: CLLocation) {
      pins.append(PinLocation(coordinate: location.coordinate))
    }

    func updateRegion(location: CLLocation) {
      region = MKCoordinateRegion(
        center: location.coordinate,
        span: MKCoordinateSpan(latitudeDelta: 0.0015, longitudeDelta: 0.0015))
    }

    func startStopLocationTracking() {
      isLocationTrackingEnabled.toggle()
      if isLocationTrackingEnabled {
        enable()
      } else {
        disable()
      }
    }
  }

  struct PinLocation: Identifiable {
    let id = UUID()
    var coordinate: CLLocationCoordinate2D
  }
}

6. CompleteTaskModel.swift

import Combine
import SwiftUI

extension CompleteTaskView {
  class Model: ObservableObject {
    @Published var isTaskExecuting = false
    @Published var resultsMessage = initialMessage

    static let initialMessage = "Fibonacci Computations"
    static let maxValue = NSDecimalNumber(mantissa: 1, exponent: 40, isNegative: false)

    var previous = NSDecimalNumber.one
    var current = NSDecimalNumber.one
    var position: UInt = 1
    var backgroundTask: UIBackgroundTaskIdentifier = .invalid
    var updateTimer: Timer?

    func beginPauseTask() {
      isTaskExecuting.toggle()
      if isTaskExecuting {
        resetCalculation()
        updateTimer = Timer.scheduledTimer(withTimeInterval: 0.5, repeats: true) { [weak self] _ in
          self?.calculateNextNumber()
        }
      } else {
        updateTimer?.invalidate()
        updateTimer = nil
        endBackgroundTaskIfActive()
        resultsMessage = Self.initialMessage
      }
    }

    func registerBackgroundTask() {
      backgroundTask = UIApplication.shared.beginBackgroundTask { [weak self] in
        print("iOS has signaled time has expired")
        self?.endBackgroundTaskIfActive()
      }
    }

    func endBackgroundTaskIfActive() {
      let isBackgroundTaskActive = backgroundTask != .invalid
      if isBackgroundTaskActive {
        print("Background task ended.")
        UIApplication.shared.endBackgroundTask(backgroundTask)
        backgroundTask = .invalid
      }
    }

    func resetCalculation() {
      previous = .one
      current = .one
      position = 1
    }

    func calculateNextNumber() {
      let result = current.adding(previous)

      if result.compare(Self.maxValue) == .orderedAscending {
        previous = current
        current = result
        position += 1
      } else {
        // This is just too much.... Start over.
        resetCalculation()
      }

      resultsMessage = "Position \(self.position) = \(self.current)"

      switch UIApplication.shared.applicationState {
      case .background:
        let timeRemaining = UIApplication.shared.backgroundTimeRemaining
        if timeRemaining < Double.greatestFiniteMagnitude {
          let secondsRemaining = String(format: "%.1f seconds remaining", timeRemaining)
          print("App is backgrounded - \(resultsMessage) - \(secondsRemaining)")
        }
      default:
        break
      }
    }

    func onChangeOfScenePhase(_ newPhase: ScenePhase) {
      switch newPhase {
      case .background:
        let isTimerRunning = updateTimer != nil
        let isTaskUnregistered = backgroundTask == .invalid

        if isTimerRunning && isTaskUnregistered {
          registerBackgroundTask()
        }
      case .active:
        endBackgroundTaskIfActive()
      default:
        break
      }
    }
  }
}

7. ContentView.swift

import SwiftUI

struct ContentView: View {
  var body: some View {
    TabView {
      AudioView()
        .tabItem {
          VStack {
            Image(systemName: "music.note")
            Text("Audio")
          }
        }
        .tag(0)

      LocationView()
        .tabItem {
          VStack {
            Image(systemName: "mappin")
            Text("Location")
          }
        }
        .tag(1)

      CompleteTaskView()
        .tabItem {
          VStack {
            Image(systemName: "platter.filled.bottom.and.arrow.down.iphone")
            Text("Completion")
          }
        }
        .tag(2)

      RefreshView()
        .tabItem {
          VStack {
            Image(systemName: "arrow.clockwise.circle")
            Text("Refresh")
          }
        }
        .tag(3)
    }
  }
}

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}

8. AudioView.swift

import SwiftUI
import AVFoundation

struct AudioView: View {
  @StateObject var model = Model()

  var body: some View {
    VStack(alignment: .center, spacing: 20) {
      Text("Audio Player")
        .font(.largeTitle)
        .fontWeight(.bold)
        .padding(EdgeInsets(top: 50, leading: 50, bottom: 0, trailing: 50))

      Spacer()

      Button(
        action: model.playPauseAudio) {
          VStack {
            Text(model.isPlaying ? "Pause" : "Play")
              .padding()
            Image(systemName: model.isPlaying ? "pause" : "play")
          }
      }
      .font(.title)
      .padding()

      Text("Now Playing: \(model.itemTitle)")
        .font(.title2)

      Text(Self.formatter.string(from: model.time) ?? "")
        .font(.title2)

      Spacer()
      Spacer()
    }
  }

  static let formatter: DateComponentsFormatter = {
    let formatter = DateComponentsFormatter()
    formatter.unitsStyle = .positional
    formatter.allowedUnits = [.minute, .second]
    formatter.zeroFormattingBehavior = .pad
    return formatter
  }()
}

struct AudioView_Previews: PreviewProvider {
  static var previews: some View {
    AudioView()
  }
}

9. LocationView.swift

import SwiftUI
import CoreLocation
import MapKit

struct LocationView: View {
  @StateObject var model = Model()

  var body: some View {
    VStack(alignment: .center, spacing: 20) {
      Text("Location Tracker")
        .font(.largeTitle)
        .fontWeight(.bold)
        .padding(EdgeInsets(top: 50, leading: 50, bottom: 0, trailing: 50))

      Button(
        action: { model.startStopLocationTracking() },
        label: {
          VStack {
            Image(systemName: model.isLocationTrackingEnabled ? "stop" : "location")
            Text(model.isLocationTrackingEnabled ? "Stop" : "Start")
          }
        })
      .font(.title)
      .padding(EdgeInsets(top: 10, leading: 10, bottom: 10, trailing: 10))

      Map(coordinateRegion: $model.region, annotationItems: model.pins) { pin in
        MapPin(coordinate: pin.coordinate, tint: .red)
      }
      .padding(EdgeInsets(top: 20, leading: 20, bottom: 20, trailing: 20))
    }
  }
}

struct LocationView_Previews: PreviewProvider {
  static var previews: some View {
    LocationView()
  }
}

10. CompleteTaskView.swift

import SwiftUI

struct CompleteTaskView: View {
  @Environment(\.scenePhase) var scenePhase
  @StateObject var model = Model()

  var body: some View {
    VStack(alignment: .center, spacing: 20) {
      Text("Task Completion")
        .font(.largeTitle)
        .fontWeight(.bold)
        .padding(EdgeInsets(top: 50, leading: 50, bottom: 0, trailing: 50))

      Spacer()

      Button(
        action: { model.beginPauseTask() },
        label: {
          VStack {
            Text(model.isTaskExecuting ? "Stop Task" : "Begin Task")
              .padding()
            Image(systemName: model.isTaskExecuting ? "stop" : "play")
          }
        })
      .font(.title)
      .padding()

      Text(model.resultsMessage)
        .font(.title2)

      Spacer()
      Spacer()
    }
    .onChange(of: scenePhase) { newPhase in
      model.onChangeOfScenePhase(newPhase)
    }
  }
}

struct FinishTaskView_Previews: PreviewProvider {
  static var previews: some View {
    CompleteTaskView()
  }
}

11. RefreshView.swift

import SwiftUI
import BackgroundTasks

struct RefreshView: View {
  @AppStorage(UserDefaultsKeys.lastRefreshDateKey) var lastRefresh = "Never"
  @Environment(\.scenePhase) var scenePhase

  var body: some View {
    VStack(alignment: .center, spacing: 20) {
      Text("Background Refresh")
        .font(.largeTitle)
        .fontWeight(.bold)
        .padding(EdgeInsets(top: 50, leading: 50, bottom: 0, trailing: 50))

      Spacer()

      Text("Refresh last performed:")
        .multilineTextAlignment(.center)
        .font(.title)
        .onChange(of: scenePhase) { scenePhase in
          if scenePhase == .background {
            print("moved to background")
          }
        }
        .padding()

      Text(lastRefresh)
        .font(.title2)

      Spacer()
      Spacer()
    }
  }
}

struct FetchView_Previews: PreviewProvider {
  static var previews: some View {
    RefreshView()
  }
}

後記

本篇主要講述了Background Modes幾種Mode使用示例，感興趣的給個贊或者關注~~~