swift - 未调用 beginGeneratingPlaybackNotifications

Question

beginGeneratingPlaybackNotifications 似乎没有在我的应用程序中被调用。我可以获取 storeIds 并且正在播放音乐（我可以向前和向后跳过），但似乎从未调用过通知。有什么建议或有什么我想念的吗？

        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

Answer 1

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

至

  object: nil

同时。