iOS 音乐应用更改状态时如何收到通知

Question

我已经尝试了所有可能的订阅方法，但没有收到任何通知

let musicPlayer = MPMusicPlayerController.systemMusicPlayer
let appMusicPlayer = MPMusicPlayerController.applicationMusicPlayer
let queuePlayer = MPMusicPlayerController.applicationQueuePlayer

func subscribe() {


    MPMediaLibrary.requestAuthorization { _ in }      

    musicPlayer.beginGeneratingPlaybackNotifications()
    appMusicPlayer.beginGeneratingPlaybackNotifications()
    queuePlayer.beginGeneratingPlaybackNotifications()

    NotificationCenter.default.addObserver(forName: .MPMusicPlayerControllerPlaybackStateDidChange, object: musicPlayer, queue: .main) { [weak self] notification in
        debugPrint("hello")
    }
    
    NotificationCenter.default.addObserver(forName: .MPMusicPlayerControllerPlaybackStateDidChange, object: appMusicPlayer, queue: .main) { [weak self] notification in
        debugPrint("hello")
    }
    
    NotificationCenter.default.addObserver(forName: .MPMusicPlayerControllerPlaybackStateDidChange, object: queuePlayer, queue: .main) { [weak self] notification in
        debugPrint("hello")
    }

    NotificationCenter.default.addObserver(
        self,
        selector: #selector(playbackStateChanged(_:)),
        name: .MPMusicPlayerControllerPlaybackStateDidChange,
        object: musicPlayer
    )

    NotificationCenter.default.addObserver(
        self,
        selector: #selector(playbackStateChanged(_:)),
        name: .MPMusicPlayerControllerPlaybackStateDidChange,
        object: appMusicPlayer
    )

    NotificationCenter.default.addObserver(
        self,
        selector: #selector(playbackStateChanged(_:)),
        name: .MPMusicPlayerControllerPlaybackStateDidChange,
        object: queuePlayer
    )

}

Answer 1

• 将“NSAppleMusicUsageDescription”添加到您的 .plist 文件中并包含字符串值 这描述了为什么您需要访问媒体播放器框架。

• 使用示例代码

  
  
  import SwiftUI
  import MediaPlayer
  
  struct ContentView: View {
      var body: some View {
          VStack {
              Image(systemName: "globe")
                  .imageScale(.large)
                  .foregroundStyle(.tint)
              Text("SetupMusic").onTapGesture {
                  setup()
              }
          }
          .padding()
      }
  }
  
  private func setup() {
      debugPrint("Rquesting access")
      MPMediaLibrary.requestAuthorization { permission in
          debugPrint("Setting up music player")
          let musicPlayer = MPMusicPlayerController.systemMusicPlayer
          musicPlayer.beginGeneratingPlaybackNotifications()
          musicPlayer.beginGeneratingPlaybackNotifications()
          debugPrint("Intial State: \(musicPlayer.playbackState)")
          NotificationCenter.default.addObserver(forName: .MPMusicPlayerControllerPlaybackStateDidChange, object: musicPlayer, queue: .main) {  notification in
              debugPrint("State changed to \(musicPlayer.playbackState)")
          }
      }
  }
  
  #Preview {
      ContentView()
  }
  
  
  

1. 在真实的 iOS 设备上运行应用程序。模拟器不支持MPMediaPlayer 框架。
2. 点击按钮以允许许可。
3. 一旦获得授权，您应该获得初始状态。 （停止/暂停）
4. 转到系统音乐应用程序并在收音机上播放一些内容。
5. 再次启动应用程序，您应该看到状态更改为“正在播放”
6. 向下滑动查看通知并暂停音乐，状态将更改为 已暂停
7. 仅当应用程序处于前台状态时才会触发事件。