ios - NSNotification (itemDidFinishPlaying) 中的观察者随机调用两次

Question

我在视频播放完毕后立即显示文本。我正在使用一种通知技术来实现这一点。唯一的问题是 Observer 不时被调用两次。它会触发“itemDidFinishPlaying”两次(因此会触发同名方法)。我无法预测什么时候。我不知道为什么。它看起来是随机的(我知道这听起来很奇怪)就像它工作正常一样，假设连续 15 次，下一次这种行为突然发生。我重建并运行应用程序，这次它连续运行 19 次，然后两次调用观察者，等等......不可预测。我已经尝试了所有场景来预测错误以修复它。到目前为止这是不可能的。所以我有 2 个问题。

1) 为什么它会“随机”发生？

2) 如何解决这个双重调用问题？

此外，以下 2 个对话也没有帮助:

Why the Observer in NSNotification called twice....?

How to stop the Observer in NSNotification to called twice?

请在下面找到我的代码:

- (void) playAnimation: (NSString *) theString {

UIView *thisCurrentView = self.currentView;
UIView *thisReplacementView = [[UIView alloc] init];

//[avPlayer pause];
[self replaceView: thisCurrentView withView: thisReplacementView];

NSString *filepath = [[NSBundle mainBundle] pathForResource:theString ofType:@"mov"];
NSURL *fileURL = [NSURL fileURLWithPath:filepath];


 // First create an AVPlayerItem
 AVPlayerItem* playerItem = [AVPlayerItem playerItemWithURL:fileURL];

 // Subscribe to the AVPlayerItem's DidPlayToEndTime notification.
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(itemDidFinishPlaying) name:AVPlayerItemDidPlayToEndTimeNotification object:playerItem];

 // Pass the AVPlayerItem to a new player
 controlledPlayer = [[AVPlayer alloc] initWithPlayerItem:playerItem];


AVPlayerLayer *animatedLayer = [AVPlayerLayer playerLayerWithPlayer:controlledPlayer];


[animatedLayer setFrame:CGRectMake(0, 0, 1024, 1024)];
[thisReplacementView.layer addSublayer: animatedLayer];


// Begin playback
[controlledPlayer play];

// Clear some content
[self displayNoContent];

pageContent = theString;


playingStatus = YES;

-(void)itemDidFinishPlaying {

[self displayContent: pageContent];

Answer 1

试试这个，

-(void)itemDidFinishPlaying {

      [self displayContent: pageContent];
      [[NSNotificationCenter defaultCenter] removeObserver:self name:AVPlayerItemDidPlayToEndTimeNotification object:playerItem];

}

它可能对你有用。

编辑 1:

每次设置新的通知观察者之前，请删除通知观察者。尝试下面的场景。它将确保删除以前的观察者(即使它不存在也没有问题)并添加新的观察者。

// Subscribe to the AVPlayerItem's DidPlayToEndTime notification.

[[NSNotificationCenter defaultCenter] removeObserver:self name:AVPlayerItemDidPlayToEndTimeNotification object:playerItem];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(itemDidFinishPlaying) name:AVPlayerItemDidPlayToEndTimeNotification object:playerItem];