监视,一旦改变执行下边的方法

- (void)viewDidLoad
{
    [super viewDidLoad];
	// Do any additional setup after loading the view, typically from a nib.
    self.p=[[Person alloc] init];
    self.p.name=@"Kim";
    self.p.age=@"18";
    
    [self.p addObserver:self forKeyPath:@"name" options: NSKeyValueObservingOptionNew context:@"132"];
    
    
    
}

方法

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

    NSLog(@"keyPath:%@",keyPath);
    NSLog(@"object:%@",object);
    NSLog(@"changge:%@",change);
    NSLog(@"context:%@",context);
    self.view.backgroundColor=[UIColor redColor];

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

}