ios - 我什么时候需要删除观察者

Question

我有一个自定义的 UITableViewCell，其中有一个 AVPlayer。我已将观察者添加到 playerItem 以了解视频何时结束。该单元格可以获得要播放的新文件，在这种情况下，它会用新实例替换 player 和 playerItem。以前，当我添加观察者时，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 playerItem 之前不删除观察者，一切都正常。

为什么我不需要在这种情况下移除观察者？

@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];
}

我还在 dealloc 中调用了 remove observer:

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

^{ARC 已开启。}

Answer 1

来自 Apple Developer Release Notes :

In OS X 10.11 and iOS 9.0 NSNotificationCenter and NSDistributedNotificationCenter will no longer send notifications to registered observers that may be deallocated.

这意味着您不需要从 iOS 9 或 OS X 10.11 中删除观察者。