MPMusicPlayerController不发布通知？

问题描述

我尝试使用 MPMusicPlayerController 播放音乐，我还想接收通知 MPMusicPlayerControllerPlaybackStateDidChange 。我设置我的播放器和通知注册几乎就像样例（它的工作，BTW - 它正确接收通知）：

   - （id）initWithPlaylist：（MPMediaPlaylist *）list {
 if（self = [super init]）{
 player = [MPMusicPlayerController applicationMusicPlayer]; 
 [player retain]; 
 
 NSLog（@set up player）; 
 [plaayer setQueueWithItemCollection：list]; 
 [player setShuffleMode：MPMusicShuffleModeOff]; 
 [player setRepeatMode：MPMusicRepeatModeNone]; 
 
 NSLog（@registration MPMusicPlayerController Notifications）; 
 [[NSNotificationCenter defaultCenter] addObserver：self 
 selector：@selector（handle_itemChanged :) 
 name：MPMusicPlayerControllerNowPlayingItemDidChangeNotification 
 object：nil]; 
 [[NSNotificationCenter defaultCenter] addObserver：self 
 selector：@selector（handle_stateChanged :) 
 name：MPMusicPlayerControllerPlaybackStateDidChangeNotification 
 object：nil]; 
 
 NSLog（@打开播放器通知）; 
 [player beginGeneratingPlaybackNotifications]; 
} 
} 
  

我得到了很多bupkis。方法 handle_itemChanged：和 handle_stateChanged：只是空的，除了 NSLog 语句，以显示他们被击中，它从来没有出现，他们被击中。 initWithPlaylist：中的 NSLog 语句按预期打印到日志。以上只是我的应用程序中的业务对象。它不是视图或视图控制器。

任何想法？奇怪的是， AddMusic 示例工作正常对我来说，我不能告诉我，对于

更新：我已经在我的应用程式委托中新增这一行，以查看完整的MPMusicPlayerController

  [[NSNotificationCenter defaultCenter] addObserverForName：nil object：nil queue：nil usingBlock：^（NSNotification * n） {NSLog（@notification：％@，n）;}]; 
  

解决方案

最后，我想出了答案：播放器必须在主线程上发送消息，它在回想起来有些意义，但它是完全不明显的，直到它曙光我修改了我打开的错误是一个错误的文档，因为我从来没有他们提到玩家必须在主线程上操作。

I"m trying to use the MPMusicPlayerController to play music, and I also want to receive the notification MPMusicPlayerControllerPlaybackStateDidChange. I set up my player and notification registration pretty much just like the sample (which works, BTW - it receives notifications correctly):

- (id) initWithPlaylist:(MPMediaPlaylist*)list {
    if (self = [super init]) {
        player = [MPMusicPlayerController applicationMusicPlayer];
        [player retain];

        NSLog(@"setting up player");
        [plaayer setQueueWithItemCollection:list];
        [player setShuffleMode:MPMusicShuffleModeOff];
        [player setRepeatMode:MPMusicRepeatModeNone];

        NSLog(@"registering MPMusicPlayerController Notifications");
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(handle_itemChanged:)
                                                     name:MPMusicPlayerControllerNowPlayingItemDidChangeNotification
                                                   object:nil];
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(handle_stateChanged:)
                                                     name:MPMusicPlayerControllerPlaybackStateDidChangeNotification
                                                   object:nil];

        NSLog(@"turning on player notifications");
        [player beginGeneratingPlaybackNotifications];
    }
}

I get a whole lot of bupkis. The methods handle_itemChanged: and handle_stateChanged: are just empty except for an NSLog statement to show they've been hit, and it never appears that they get hit. The NSLog statements in initWithPlaylist: are printed to the log as expected. The above is just a business object in my app. It's not a view or view controller.

Any ideas? The bizarre thing is that the AddMusic sample works just fine for me, and I can't tell that I"m doing anything differently with regard to the MPMusicPlayerController and its notifications.

Update: I've added this line in my app delegate to see the full flood of notifications:

[[NSNotificationCenter defaultCenter] addObserverForName:nil object:nil queue:nil usingBlock:^(NSNotification *n) { NSLog(@"notification: %@", n); }];

I see all kinds of notifications being printed to the console, but none from the media player controller.

解决方案

Finally, I figured out the answer: the player has to be sent messages on the main thread. It makes some sense in retrospect, but it was completely non-obvious until the moment it dawned on me. I modified the bug I opened to be a bug on the documentation because I never did spot where they mentioned that the player must be operated on the main thread.

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