Question

removeObserver是否有任何角落案例行为：name：object：？在下面的代码块中，我的观察者没有正确注册：

- (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，如果我将订单更改为：

- (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];
}

所有通知都很好。这让我相信当我打电话时会发生一些奇怪的事情：

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

我错过了一些非常明显的东西吗？我在iOS 6上没有ARC。

Answer 1

找到答案。事实证明，它与传递nil观察者名称有关。致电[[NSNotificationCenter defaultCenter] removeObserver:self name:nil object:temp]; 将删除self以免观察temp发布的任何通知。但是，在临界值为nil的情况下，这行代码将同时删除self作为观察者。

Answer 2

名称不应为零。你试过给观察者一个名字吗？

Answer 3

@Lee是正确的，名称不应该是nil，但它也不应该是观察者的名字。相反，它应该是您要注册观察的通知的名称。例如，UIDeviceOrientationDidChangeNotification。添加要在该参数中观察的通知的名称，并在删除观察者时将其作为名称参数传递

NSNotificationCenter删除了错误的观察者？

3 个答案: