键值观察者模式KVO--为UIImageView添加KVO

UIImagVIew * coverImage = nil；
/*........
........相关代码.......
........
*/

//为coverImage的image属性添加KVO，添加自己为属性变化的观察者
[coverImage addObserver:self forKeyPath:@"image" options:0 context:nil];

//KVO的回调函数，当keyPath发生变化时调用

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

{

if ([keyPath isEqualToString:@"image"]) {

//如果发生变化，进行相关处理

..........

}

}

- (void)dealloc
{

//移除观察者
[coverImage removeObserver:self forKeyPath:@"image"];
}