/*
     * @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;  
    }