KVO

    Person *p = [[Person alloc]init];

    NSLog(@"=====%@====%ld",p.name,p.age);

    [p addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew |  NSKeyValueObservingOptionOld context:NULL];

    [p addObserver:self forKeyPath:@"age" options:NSKeyValueObservingOptionNew |  NSKeyValueObservingOptionOld context:NULL];

    p.name = @"wang";

    p.age = 56;

 

}

+(BOOL)automaticallyNotifiesObserversForKey:(NSString *)key{

    if ([key isEqualToString:@"name"]) {

        return NO;

    }

    return [super automaticallyNotifiesObserversForKey:key];

}

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

    NSLog(@"%@===%@====%@====%@=",keyPath,object,change[@"new"],context);

}