iOS 添加监听

    self.abserveStr =@"123";

    [selfaddObserver:selfforKeyPath:@"abserveStr"options:NSKeyValueObservingOptionOldcontext:nil];

    self.abserveStr =@"456";

    self.abserveStr =@"789";

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context

{

    NSLog(@"~~~~%@",self.abserveStr);

    for (NSString *keyin change) {

        NSLog(@"--- %@: %@",key,[changeobjectForKey:key]);

    }

}

- (void)dealloc

{

    [selfremoveObserver:selfforKeyPath:@"abserveStr"];

}

输出结果：

2017-09-05 10:02:56.481 DCLProject[1662:495473] ~~~~456

2017-09-05 10:02:56.481 DCLProject[1662:495473] --- kind: 1

2017-09-05 10:02:56.481 DCLProject[1662:495473] --- old: 123

2017-09-05 10:02:56.481 DCLProject[1662:495473] ~~~~789

2017-09-05 10:02:56.481 DCLProject[1662:495473] --- kind: 1

2017-09-05 10:02:56.481 DCLProject[1662:495473] --- old: 456

说明

- (void)addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(nullable void *)context;

observer:观察对象self

keyPath:所观察的观察属性

options:NSKeyValueObservingOptionOld 可以参考输出

context：nil

记得在delloc中移除