objective-c – 使用NSMutableArray的KVO

我的AppDelegate中有一个名为blocks的NSMutableArray属性.
每当一个对象被添加到这个数组时我想观察.
我读过其他帖子,但我不明白为什么这不起作用.

在我的app委托类中,我实现了

- (void)insertObject:(id)obj inBlocksAtIndex:(NSInteger)index
{
    [blocks insertObject:obj atIndex:index];
}

在我的视图控制器的init方法中,我将一个观察者添加到我的AppDelegate引用中.

boardModel = [[UIApplication sharedApplication] delegate];
[boardModel addObserver:self forKeyPath:@"blocks" options:0 context:NULL];

在我的视图控制器的viewDidLoad方法中,我尝试调用我之前实现的KVO索引数组访问器,

[boardModel insertObject:[[Block alloc] init] inBlocksAtIndex:0];

然后我实现我的observeValueForKeyPath方法：

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if ([keyPath isEqualToString:@"blocks"])
    {
        NSLog(@"ADDED");
    }
}

我已经尝试在observeValueForKeyPath中的if语句之前添加一个NSLog语句,似乎它永远不会被调用.

我也尝试了NSLogging [[boardModel blocks] count],它说计数为1(正在添加对象).

我肯定错过了什么.

// This will fire KVO as you're changing the app delegate's `blocks` property.
appDelegate.blocks = [NSMutableArray array];

// This will not fire KVO as the app delegate's `blocks` property still points
// to the same object; from the app delegate's perspective,nothing's happened.
[appDelegate.blocks addObject:@"Object"];

[boardModel.blocks addObserver:self forKeyPath:@"count" options:0 context:NULL];