self.model=[[DataModel alloc]init]; [self.model setValue:@"searph" forKey:@"stockName"]; [self.model setValue:@"10.0" forKey:@"price"]; [self.model addObserver:self forKeyPath:@"price" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil]; self.myLabel=[[UILabel alloc]initWithFrame:CGRectMake(100, 100, 100, 30)]; self.myLabel.layer.masksToBounds=YES; self.myLabel.layer.cornerRadius=50; self.myLabel.textColor=[UIColor cyanColor]; self.myLabel.text=[self.model valueForKey:@"price"]; [self.view addSubview:self.myLabel]; self.myButton=[UIButton buttonWithType:UIButtonTypeRoundedRect]; self.myButton.frame=CGRectMake(200,200 , 100, 30); [self.myButton addTarget:self action:@selector(changeValue) forControlEvents:UIControlEventTouchUpInside]; [self.myButton setBackgroundColor:[UIColor lightGrayColor]]; [self.view addSubview:self.myButton];}- (void)changeValue{ [self.model setValue:@"20.0" forKey:@"price"];}- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{ if ([keyPath isEqualToString:@"price"]) { self.myLabel.text=[self.model valueForKey:@"price"]; }}
程序运行之后就报错
*** Terminating app due to uncaught exception ‘NSUnknownKeyException’, reason: ‘[<DataModel 0x7fe44bf22810> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key price.’
检查之后发现self.myLabel.text=[self.model valueForKey:@"price"];改为self.myLabel.text=[NSString stringWithFormat:@"%@",[self.model valueForKey:@"price"]];即可
，勇敢的冷静的理智的去接受失败，有时不但是必要的，而且是很有必要的。
