//记录access token 申请时的时间

         private static DateTime GetAccessToken_Time;  

         /// <summary>

         /// 过期时间为7200秒

         /// </summary>

         private static int Expires_Period = ;

 　　　　　　private static string mAccessToken;

         /// <summary>

         /// 获取access token

         /// </summary>

         /// <returns></returns>

         private static string GetAccessToken()

         {

             if (string.IsNullOrEmpty(mAccessToken) || HasExpired())

             {

                 string Url = "https://api.weixin.qq.com/cgi-bin/token";

                 string RequestPara = "grant_type=client_credential&appid=" + APPID + "&secret=" + APPSECRET;

                 string result = WebRequestHelper.GetData(RequestPara, Url);

                 if (!result.Equals(""))

                 {

                     GetAccessToken_Time = DateTime.Now;

                     accesstoken token = JsonFormat.Deserialize<accesstoken>(result);

                     Expires_Period = Convert.ToInt32(token.expires_in);

                     return token.access_token;

                 }

                 else

                 {

                     GetAccessToken_Time = DateTime.MinValue;

                 }

             }

             return null;

         }

         /// <summary>

         /// 判断Access_token是否过期

         /// </summary>

         /// <returns>bool</returns>

         private static bool HasExpired()

         {

             if (GetAccessToken_Time != null)

             {

                 //过期时间，允许有一定的误差，一分钟。获取时间消耗

                 if (DateTime.Now > GetAccessToken_Time.AddSeconds(Expires_Period).AddSeconds(-))

                 {

                     return true;

                 }

             }

             return false;

         }