ios - NSNotificationCenter 删除错误的观察者？

Question

removeObserver:name:object: 是否有任何极端情况行为？在以下代码块中，我的观察者未正确注册:

- (void)setPlayerItem:(AVPlayerItem *)playerItem {
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(playerItemDidReachEnd:)
                                                 name:nil
                                               object:playerItem];

    [playerItem addObserver:self
                 forKeyPath:kStatus
                    options:0
                    context:(__bridge void*)self];

    [playerItem addObserver:self
                 forKeyPath:kPlaybackBufferEmpty
                    options:0
                    context:(__bridge void*)self]; // For adding a buffering activity indicator

    id temp = playerItem_;
    playerItem_ = [playerItem retain];

    [[NSNotificationCenter defaultCenter] removeObserver:self name:nil object:temp];
    [temp removeObserver:self forKeyPath:kPlaybackBufferEmpty];
    [temp removeObserver:self forKeyPath:kStatus];
    [temp release];
}

但是，如果我将顺序更改为:

- (void)setPlayerItem:(AVPlayerItem *)playerItem {    
    [playerItem addObserver:self
                 forKeyPath:kStatus
                    options:0
                    context:(__bridge void*)self];

    [playerItem addObserver:self
                 forKeyPath:kPlaybackBufferEmpty
                    options:0
                    context:(__bridge void*)self]; // For adding a buffering activity indicator

    id temp = playerItem_;
    playerItem_ = [playerItem retain];

    [[NSNotificationCenter defaultCenter] removeObserver:self name:nil object:temp];
    [temp removeObserver:self forKeyPath:kPlaybackBufferEmpty];
    [temp removeObserver:self forKeyPath:kStatus];
    [temp release];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(playerItemDidReachEnd:)
                                                 name:nil
                                               object:playerItem];
}

所有通知都发布得很好。这让我相信当我打电话时发生了奇怪的事情:

    [[NSNotificationCenter defaultCenter] removeObserver:self name:nil object:temp];

我在这里遗漏了一些非常明显的东西吗？我使用的是没有 ARC 的 iOS 6。

Answer 1

找到答案了。事实证明，这与传入观察者名称的 nil 有关。 调用[[NSNotificationCenter defaultCenter]removeObserver:self name:nil object:temp]; 将使 self 不再观察 temp 发布的任何通知。 然而，在 temp 为 nil 的极端情况下，这行代码将把 self 作为观察者全部删除。