iOS NSDictionary JSON 相互转换

/*!  
 * @brief 把格式化的JSON格式的字符串转换成字典  
 * @param jsonString JSON格式的字符串  
 * @return 返回字典  
 */  
+ (NSDictionary *)dictionaryWithJsonString:(NSString *)jsonString {  
    if (jsonString == nil) {  
        return nil;  
    }  
      
    NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];  
    NSError *err;  
    NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:jsonData  
                                                        options:NSJSONReadingMutableContainers  
                                                          error:&err];  
    if(err) {  
        NSLog(@"json解析失败：%@",err);  
        return nil;  
    }  
    return dic;  
}  

/**
 *  字段转换成json字符串
 *
 *  @param dict <#dict description#>
 *
 *  @return <#return value description#>
 */
+(NSString *)dictToJsonStr:(NSDictionary *)dict{
    
//    NSMutableDictionary *dict = [NSMutableDictionary new];
//    [dict setObject:@"" forKey:@"AWL_LAN"];
//    [dict setObject:@"" forKey:@"AWL_LON"];
//    [dict setObject:@"1"  forKey:@"U_ID"];
    NSString *jsonString = nil;
    if ([NSJSONSerialization isValidJSONObject:dict])
    {
        NSError *error;
        NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dict options:NSJSONWritingPrettyPrinted error:&error];
        jsonString =[[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
        //NSLog(@"json data:%@",jsonString);
        if (error) {
            NSLog(@"Error:%@" , error);
        }
    }
    return jsonString;
}