KVO

//监听-(instancetype)init{        self = [super init];        if (self)    {                self.name = @"帅帅哒";                //注册监听//        NSKeyValueObservingOptionNew//        NSKeyValueObservingOptionOld        [self addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];            }        return self;    }//监听回调方法-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary*)change context:(void *)context

{

NSLog(@"新值:%@!",change[@"new"]);

NSLog(@"旧值:%@!",change[@"old"]);

}

//移除监听

-(void)dealloc

{

[self removeObserver:self forKeyPath:@"name"];

}

main.m

Person *person = [[Person alloc]init];

person.name = @"😡";