Objective-c key-value observer KVO mode Learning

The KVO key-value observer mode is an important mechanism of cocoa similar to the notification mode. When the attributes of the observer change, the observer performs corresponding operations.

Create a new person class to inherit nsobject, add the name and age attributes, and then create a personobserver class to inherit nsobject at the same time

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

Method

The details are as follows:

- (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];}

Use keypath to determine whether the property of our listener has changed. If yes, perform the corresponding operation.

Add an observer to an object:

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"];

Running effect:

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