KVO

使用步骤:

    1>.添加监听器

    // 利用b对象来监听a对象name属性的改变

    [a addObserver:b forKeyPath:@"name" options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew context:@"test"];

 

    2>.在监听器中实现监听方法

    -(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change     context:(void *)context

    {

        NSLog(@"%@ %@ %@ %@", object, keyPath, change, context);

    }
　　3>.移除监听

　　[a removeObserver];