KVO监听数据模型

监听一个model值得变化

    [self.model addObserver:self forKeyPath:@"note" options:NSKeyValueObservingOptionNew context:nil];

重写方法ObserveValueForkeypath方法

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context{    NSLog(@"keyPath %@",keyPath);    NSLog(@"被修改的对象  %@",object);    NSLog(@"被修改的值  %@",[change objectForKey:@"new"]);    NSLog(@"被修改的上下文 %@",context);}

移除

-(void)dealloc{    [self.model removeObserver:self forKeyPath:@"note"];}