@interface FoodData : NSObject

{

    NSString * foodName;

    float foodPrice;    

}

@end

////////////////////////////////////////////////////////////////////////////

foodData = [[FoodDataalloc]init];

    [foodDataaddObserver:selfforKeyPath:@"foodName"options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOldcontext:nil];

    [foodDataaddObserver:selfforKeyPath:@"foodPrice"options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOldcontext:nil];

    ///调用

    [foodDatasetValue:@"apple"forKey:@"foodName"];

    [foodDatasetValue:@"100.0"forKey:@"foodPrice"];

///////响应

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

{

    if( [keyPath isEqualToString:@"foodName"])

    {

        NSLog(@"foodName:%@",[foodDatavalueForKey:@"foodName"]);

    }

    else if( [keyPath isEqualToString:@"foodPrice"])

    {

         NSLog(@"foodPrice:%@",[foodDatavalueForKey:@"foodPrice"]);

    }

}