ios kvo 的用法

  [selfaddObserver:selfforKeyPath:@"Ab"options:NSKeyValueObservingOptionNew context:nil];

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

    NSLog(@"%@",keyPath);

    if ([keyPathisEqualToString:@"Ab"]) {

        NSLog(@"change====%@",change);

        

        NSLog(@"new==%@",[changevalueForKey:@"new"]);

        

    }

}