我什么时候需要删除观察者

我有一个定制UITableViewCell的AVPlayer内容.我添加了观察者,playerItem以了解视频何时到达终点.该细胞可以得到一个新的文件进行播放,在这种情况下,它取代了player与playerItem新的实例.在以前我添加观察者时,我必须在dealloc中删除它,否则应用程序会崩溃.

这一次,我注意到即使我在删除之前没有移除观察者,playerItem一切正常.

在这种情况下,为什么我不需要删除观察者？

@interface CallResultTableViewCell : UITableViewCell

@property (nonatomic, strong) AVPlayer *player;
@property (nonatomic, strong) AVPlayerItem *playerItem;
@property (nonatomic, strong) NSURL *url;

-(void) embedUrl:(NSURL *)url;

@end

-(void) embedUrl:(NSURL *)url {
    if (self.url == nil || ![self.url isEqual:url]) {
        if (self.player != nil) {
            [self.player pause];
            self.player = nil;
            //[[NSNotificationCenter defaultCenter] removeObserver:self
            //                                                name:AVPlayerItemDidPlayToEndTimeNotification
            //                                              object:self.playerItem];
            self.playerItem = nil;
            //...
        }
        if (url != nil) {
            self.playerItem = [myUrls playerItemWithURL:url];
            self.player = [AVPlayer playerWithPlayerItem:self.playerItem];
            self.url = url;
            //...
            [[NSNotificationCenter defaultCenter] addObserver:self
                                                     selector:@selector(itemDidFinishPlaying:)
                                                         name:AVPlayerItemDidPlayToEndTimeNotification
                                                       object:self.playerItem];
        }
    }
    [self.player play];
}

-(void)itemDidFinishPlaying:(NSNotification *) notification {
    [self.playerItem seekToTime:kCMTimeZero];
    [self.player play];
}

我还呼吁remove observer在dealloc:

-(void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self
                                                    name:AVPlayerItemDidPlayToEndTimeNotification
                                                  object:self.playerItem];
}

^{ARC已开启.}

来自Apple Developer发行说明:

在OS X 10.11和iOS 9.0中,NSNotificationCenter和NSDistributedNotificationCenter将不再向可能已解除分配的已注册观察者发送通知.

这意味着您无需从iOS 9或OS X 10.11中删除观察者.