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
*** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<DataModel 0x7fe44b
原文：http://blog.csdn.net/darongzi1314/article/details/45152607
