objective-c 索引值觀察者KVO模式的學習

KVO 索引值觀察者模式是cocoa的一個重要機制類似Notification模式。當被觀察者屬性發生改變時觀察者做相應的操作。

建立一個Person類繼承NSObject，添加name和age屬性，接著建一個PersonObserver類繼承於NSObject同時實現

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

方法

具體如下：

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{    if ([keyPath isEqualToString:kPathName]) {        NSLog(@"old name:%@ \nnew name:%@", [change objectForKey:@"old"], [change objectForKey:@"new"]);                //Do something what you want to do        //...        return;    }    [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];}

利用keyPath判斷是否是我們監聽的屬性發生了變化，如果是做相應的操作。

為對象添加觀察者：

Person *person = [[Person alloc] init];    [person setName:@"old name"];    PersonObserver *observer = [[PersonObserver alloc] init];        [person addObserver:observer forKeyPath:@"name" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];        [person setName:@"new name"];        [person removeObserver:observer forKeyPath:@"name"];

運行效果：

2013-03-05 16:08:04.347 learnOcKVO[10980:11303] old name:old name new name:new name