KVO的使用(键值监听)

stockForKVO = [[StockData alloc] init];  
    [stockForKVO setValue:@"searph" forKey:@"stockName"];  
    [stockForKVO setValue:@"10.0" forKey:@"price"];      
    [stockForKVO addObserver:self forKeyPath:@"price" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL]; 

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if([keyPath isEqualToString:@"price"])
    {
        myLabel.text = [stockForKVO valueForKey:@"price"];
    }
}

- (void)dealloc
{
    [super dealloc];
    [stockForKVO removeObserver:self forKeyPath:@"price"];
    [stockForKVO release];
}