如何监听iOS音乐应用状态变更？订阅通知失败求助

问题重现 #

已尝试多种订阅方式，但仍无法收到iOS系统音乐应用的播放状态变更通知，实现代码如下：

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
    )
}

核心问题与解决步骤 #

1. 聚焦正确的播放器实例
   applicationMusicPlayer和applicationQueuePlayer是应用内专属播放器，仅响应自身应用内的播放操作，不会监听系统音乐App的状态变化。只需保留systemMusicPlayer的相关配置，移除另外两个播放器的通知订阅和beginGeneratingPlaybackNotifications调用。

2. 确保权限配置完整

   • 在Info.plist中添加NSAppleMusicUsageDescription键，填写合理的权限申请理由（如"需要获取音乐播放状态"），否则授权会直接失败。
   • 等待授权结果返回后再初始化播放器和订阅通知，不要调用requestAuthorization后立即执行后续操作：

     MPMediaLibrary.requestAuthorization { status in
         guard status == .authorized else { return }
         DispatchQueue.main.async {
             self.musicPlayer.beginGeneratingPlaybackNotifications()
             self.setupNotifications()
         }
     }
     

3. 优化通知订阅逻辑
   无需同时使用闭包和Selector两种订阅方式，选择一种即可避免冗余。比如保留闭包方式：

   func setupNotifications() {
       NotificationCenter.default.addObserver(forName: .MPMusicPlayerControllerPlaybackStateDidChange, object: musicPlayer, queue: .main) { [weak self] _ in
           debugPrint("播放状态变更")
           // 在此处理状态变更逻辑
       }
   }
   

4. 保证播放器实例的生命周期
   将musicPlayer声明为全局变量或类的属性（如ViewController的属性），确保不会被提前释放，否则通知订阅会失效。

5. 正确测试场景
   测试时需在系统音乐App中操作播放、暂停、切歌，而非在自身应用内测试，systemMusicPlayer仅同步系统音乐的状态变化。

内容的提问来源于stack exchange，提问作者erotsppa