Swift 未调用BegingeratingPlaybackNotifications

BegingeratingPlaybackNotifications似乎没有在我的应用程序中调用。我可以获取StoreID，音乐正在播放（我可以向前和向后跳过），但通知似乎从未被调用。有什么建议或是我遗漏了什么

        let player = MPMusicPlayerController.applicationQueuePlayer

        // Trying all of these
        player.beginGeneratingPlaybackNotifications()
        MPMusicPlayerController.systemMusicPlayer.beginGeneratingPlaybackNotifications()
        MPMusicPlayerController.applicationMusicPlayer.beginGeneratingPlaybackNotifications()
        MPMusicPlayerController.applicationQueuePlayer.beginGeneratingPlaybackNotifications()

        NotificationCenter.default.addObserver(self,
                                               selector: #selector(refreshView),
                                               name: .MPMusicPlayerControllerPlaybackStateDidChange,
                                               object: self)


        NotificationCenter.default.addObserver(self,
                                               selector: #selector(refreshView),
                                               name: .MPMusicPlayerControllerNowPlayingItemDidChange,
                                               object: self)

    let queue  = MPMusicPlayerStoreQueueDescriptor(storeIDs: storeIds)
    player.setQueue(with: queue)
    player.play()

    // Never called
    @objc func refreshView(){
      let nowPlaying = player.nowPlayingItem

这些线路是错误的：

    NotificationCenter.default.addObserver(self,
                                           selector: #selector(refreshView),
                                           name: .MPMusicPlayerControllerPlaybackStateDidChange,
                                           object: self)


    NotificationCenter.default.addObserver(self,
                                           selector: #selector(refreshView),
                                           name: .MPMusicPlayerControllerNowPlayingItemDidChange,
                                           object: self)

改变

  object: self

到

两者都有

这些行是错误的：

    NotificationCenter.default.addObserver(self,
                                           selector: #selector(refreshView),
                                           name: .MPMusicPlayerControllerPlaybackStateDidChange,
                                           object: self)


    NotificationCenter.default.addObserver(self,
                                           selector: #selector(refreshView),
                                           name: .MPMusicPlayerControllerNowPlayingItemDidChange,
                                           object: self)

改变

  object: self

到

两者都有