如果 iPodMusicPlayer 在后台创建，则不会发送通知

Question

如果 iPodMusicPlayer 是在后台创建的，那么我不会发送有关播放状态更改的通知。

这是代码：

- (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];
}

有什么方法可以在后台创建 iPodMusicPlayer 吗？否则，如果它是在主线程上创建的，它会阻塞执行一段时间。

Answer 1

音乐播放器必须在主线程上使用。

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