/// <summary>
        /// 生成图文信息Json
        /// </summary>
        /// <param name="Messageid"></param>
        /// <returns></returns>
        public static string GetArticlesJsonStr(Guid Messageid)
        {
            WX_Message    Messages       = WX_MessageService.instance().Single(Messageid);
            StringBuilder sbArticlesJson = new StringBuilder();

            //  articles
            if (Messages.Groups.Count() > 0)
            {
                List <articles> list = new List <articles>();
                foreach (var item in Messages.Groups)
                {
                    articles a = new articles();
                    a.title              = item.Title;
                    a.author             = item.Author;
                    a.content            = item.Content;
                    a.content_source_url = item.URL;
                    a.digest             = "";
                    a.show_cover_pic     = 0;
                    a.thumb_media_id     = item.Img_media_id;
                    list.Add(a);
                }
                sbArticlesJson.Append("{\"articles\":");
                sbArticlesJson.Append(JsonHelper.SerializeObject(list));
                sbArticlesJson.Append("}");
                return(sbArticlesJson.ToString());
            }
            return("");
        }
 public static WX_MessageService instance()
 {
     if (_instance == null)
     {
         _instance = new WX_MessageService();
     }
     return(_instance);
 }