C#微信公众号开发 -- （四）获取API调用所需的全局唯一票据access_token

 public class Access_token
    {
        public Access_token()
        {
            //
            //TODO: 在此处添加构造函数逻辑
            //
        }
        string _access_token;
        string _expires_in;

        /// <summary>
        /// 获取到的凭证 
        /// </summary>
        public string access_token
        {
            get { return _access_token; }
            set { _access_token = value; }
        }


        /// <summary>
        /// 凭证有效时间，单位：秒
        /// </summary>
        public string expires_in
        {
            get { return _expires_in; }
            set { _expires_in = value; }
        }
    }

/// <summary>
        /// 根据当前日期 判断Access_Token 是否超期  如果超期返回新的Access_Token   否则返回之前的Access_Token
        /// </summary>
        /// <param name="datetime"></param>
        /// <returns></returns>
        private static string IsExistAccess_Token()
        {
            string Token = string.Empty;
            DateTime YouXRQ;
            // 读取XML文件中的数据，并显示出来 ，注意文件路径
            string filepath = HttpContext.Current.Server.MapPath(".") + "\\AccessToken.xml";

            StreamReader str = new StreamReader(filepath, Encoding.UTF8);
            XmlDocument xml = new XmlDocument();
            xml.Load(str);
            str.Close();
            str.Dispose();
            Token = xml.SelectSingleNode("xml").SelectSingleNode("Access_Token").InnerText;
            YouXRQ = Convert.ToDateTime(xml.SelectSingleNode("xml").SelectSingleNode("Access_YouXRQ").InnerText);

            //TimeSpan st1 = new TimeSpan(YouXRQ.Ticks); //最后刷新的时间
            //TimeSpan st2 = new TimeSpan(DateTime.Now.Ticks); //当前时间
            //TimeSpan st = st2 - st1; //两者相差时间
            if (DateTime.Now > YouXRQ)
            {
                DateTime _youxrq = DateTime.Now;
                Access_token mode = GetAccess_token();
                xml.SelectSingleNode("xml").SelectSingleNode("Access_Token").InnerText = mode.access_token;
                _youxrq = _youxrq.AddSeconds(int.Parse(mode.expires_in));
                xml.SelectSingleNode("xml").SelectSingleNode("Access_YouXRQ").InnerText = _youxrq.ToString();
                xml.Save(filepath);
                Token = mode.access_token;
            }
            return Token;
        }


        /// <summary>
        /// 获取Access_token
        /// </summary>
        /// <returns></returns>
        private static Access_token GetAccess_token()
        {
            string appid = "你自己微信公众测试号的appID"; //微信公众号appid
            string secret = "你自己微信公众测试号的appsecret";  //微信公众号appsecret
            string strUrl = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=" + appid + "&secret=" + secret;
            Access_token mode = new Access_token();

            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(strUrl);  //用GET形式请求指定的地址 
            req.Method = "GET";

            using (WebResponse wr = req.GetResponse())
            {
                //HttpWebResponse myResponse = (HttpWebResponse)req.GetResponse();  
                StreamReader reader = new StreamReader(wr.GetResponseStream(), Encoding.UTF8);
                string content = reader.ReadToEnd();
                reader.Close();
                reader.Dispose();

                //在这里对Access_token 赋值  
                Access_token token = new Access_token();
                token = JsonHelper.ParseFromJson<Access_token>(content);
                mode.access_token = token.access_token;
                mode.expires_in = token.expires_in;
            }
            return mode;
        }

public class JsonHelper
    {
        /// <summary>
        /// 生成Json格式
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="obj"></param>
        /// <returns></returns>
        public static string GetJson<T>(T obj)
        {
            DataContractJsonSerializer json = new DataContractJsonSerializer(obj.GetType());
            using (MemoryStream stream = new MemoryStream())
            {
                json.WriteObject(stream, obj);
                string szJson = Encoding.UTF8.GetString(stream.ToArray()); return szJson;
            }
        }
        /// <summary>
        /// 获取Json的Model
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="szJson"></param>
        /// <returns></returns>
        public static T ParseFromJson<T>(string szJson)
        {
            T obj = Activator.CreateInstance<T>();
            using (MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(szJson)))
            {
                DataContractJsonSerializer serializer = new DataContractJsonSerializer(obj.GetType());
                return (T)serializer.ReadObject(ms);
            }
        }
    }