如何在后台更新 MPNowPlayingInfoCenter 并且 AVQueuePlayer 中的轨道发生变化

Question

所以我试图在后台更新 MPNowPlayingInfoCenter 并且 AVQueuePlayer 中的轨道发生变化。

在前台很容易在

- (id) init{
 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didFinish) name:AVPlayerItemDidPlayToEndTimeNotification object:nil];

  player = [[AVQueuePlayer alloc]init];
  player.actionAtItemEnd = AVPlayerActionAtItemEndPause;
}

-(void)didFinish{
  [[NSNotificationCenter defaultCenter] removeObserver:self];
  // Magic goes here
  //[[MPNowPlayingInfoCenter defaultCenter] setNowPlayingInfo:nowPlaying]; 
  [player advanceToNextItem];
  [player play];
}

在后台但是没有 AVPlayerActionAtItemEndAdvance 它不会转到下一个，并且 AVPlayerActionAtItemEndAdvance 永远不会在后台调用 didFinish

- (id) init{
 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didFinish) name:AVPlayerItemDidPlayToEndTimeNotification object:nil];

  player = [[AVQueuePlayer alloc]init];
  player.actionAtItemEnd = AVPlayerActionAtItemEndAdvance;
}

-(void)didFinish{ //never called
  [[NSNotificationCenter defaultCenter] removeObserver:self];
  // Magic goes here
  //[[MPNowPlayingInfoCenter defaultCenter] setNowPlayingInfo:nowPlaying]; 
  //play is not needed in this case
}

谢谢！

Answer 1

使用 KVO：

[self.queuePlayer addObserver:self forKeyPath:@"currentItem" options:NSKeyValueObservingOptionNew context:PlayerItemKVOContext];

和

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {

    if (context == PlayerItemKVOContext) {
        AVPlayerItem *playerItem = [_queuePlayer currentItem];