// 1.键-值观察
// 2.它提供一种机制，当指定的对象的属性被修改后，则对象就会接受到通知。
// 3.符合KVC（Key-ValuedCoding）机制的对象才可以使用KVO
// 4.实现过程
// ①注册，指定被观察者
// ②实现回调方法
// ③移除观察
- (void)viewDidLoad{ [super viewDidLoad]; // Do any additional setup after loading the view from its nib. // 实例化一个观察者对象 self.stockForKVO = [[StockData alloc] init]; // 初始化 [self.stockForKVO setValue:@"searph" forKey:@"stockName"];// KVC [self.stockForKVO setValue:@"10.0" forKey:@"price"];// KVC // 监听并显示在 lable 里 - 注册观察者 [self.stockForKVO addObserver:self forKeyPath:@"price" options:NSKeyValueObservingOptionNew context:nil]; self.myLable.textColor = [UIColor redColor]; self.myLable.text = [self.stockForKVO valueForKey:@"price"]; // 创建 button 按钮 UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect]; [button setFrame:CGRectMake(90, 150, 140, 42)]; [button setTitle:@"按钮" forState:UIControlStateNormal]; [button addTarget:self action:@selector(buttonAction) forControlEvents:UIControlEventTouchUpInside]; [self.view addSubview:button];}// button响应方法- (void)buttonAction{ [self.stockForKVO setValue:@"20.0" forKey:@"price"];}// 回调方法- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{ if ([keyPath isEqualToString:@"price"]) { self.myLable.text = [self.stockForKVO valueForKey:@"price"]; }}- (void)dealloc{ // 移除观察者 [self.stockForKVO removeObserver:self forKeyPath:@"price"];}