//增加
        //增加新的键值对象  
    [dic setValue:@"obj3" forKey:@"key3"];  
    //增加已经存在的字典
    [dic addEntriesFromDictionary:dic1];
//修改
    //用新的字典换旧的字典
    [dic setDictionary:dic1];
    //向词典为key的键中添加obj，如果key存在则替换该值
    [dic setObject:@"obj3" forKey:@"key2"];
    dic[@"key2"] = @"obj3";
//删除
    //根据key删除obj  
    [dic removeObjectForKey:@"key1"];  
    //根据key数组删除元素  
    NSArray *arr = [dic allKeys];
    [dic removeObjectsForKeys:arr];
    //删除所有元素  
    [dic removeAllObjects];

//增加
        //增加新的键值对象  
    [dic setValue:@"obj3" forKey:@"key3"];  
    //增加已经存在的字典
    [dic addEntriesFromDictionary:dic1];
//修改
    //用新的字典换旧的字典
    [dic setDictionary:dic1];
    //向词典为key的键中添加obj，如果key存在则替换该值
    [dic setObject:@"obj3" forKey:@"key2"];
    dic[@"key2"] = @"obj3";
//删除
    //根据key删除obj  
    [dic removeObjectForKey:@"key1"];  
    //根据key数组删除元素  
    NSArray *arr = [dic allKeys];
    [dic removeObjectsForKeys:arr];
    //删除所有元素  
    [dic removeAllObjects];