如果iPodMusicPlayer在後臺創建，它不會發送通知

Question

如果在後臺創建iPodMusicPlayer，則不會發送有關播放狀態更改的通知。

這裏是代碼：

- (void)initMusicPlayer { 
    musicPlayer = [MPMusicPlayerController iPodMusicPlayer]; 

    NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter]; 
    [notificationCenter addObserver:self selector:@selector(musicPlayerStateChanged:) 
      name:MPMusicPlayerControllerNowPlayingItemDidChangeNotification 
      object:musicPlayer]; 
    [notificationCenter addObserver:self selector:@selector(musicPlayerStateChanged:) 
      name:MPMusicPlayerControllerPlaybackStateDidChangeNotification 
      object:musicPlayer]; 
    [musicPlayer beginGeneratingPlaybackNotifications]; 
} 

- (void)viewDidLoad { 
    [self performSelectorInBackground:@selector(initMusicPlayer) withObject:nil]; 
} 

是否有某種方式如何在後臺創建iPodMusicPlayer？否則，如果它是在主線程上創建的，它會暫時阻止執行。

Answer 1

必須在主線程上使用音樂播放器。

https://developer.apple.com/library/ios/#documentation/MediaPlayer/Reference/MPMusicPlayerController_ClassReference/Reference/Reference.html%23//apple_ref/doc/uid/TP40008221