微信公共服务平台开发（.Net 的实现）2-------获得ACCESSTOKEN

成为了开发者之后微信平台会给您appid和secret，在订阅号中是没有的，所以因该申请一下服务号

有了accesstoken才能做添加菜单，上传/下载图片等功能

private string gettoken()
     {

         // 也可以这样写:
         //return  getpage("https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=你的appid&secret=你的secret", "");
       
         string res = "";
         httpwebrequest req = (httpwebrequest)httpwebrequest.create("https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential
&appid=你的appid&secret=你的secret");
 req.method = "get";
         using (webresponse wr = req.getresponse())
         {
             httpwebresponse myresponse = (httpwebresponse)req.getresponse();


             streamreader reader = new streamreader(myresponse.getresponsestream(), encoding.utf8);


             string content = reader.readtoend();
   
             list myaccesstoken = json.jsonstringtolist(content);
             res = myaccesstoken[0].access_token;
 
         }


         return res;
     }
     public string getpage(string posturl, string postdata)
     {
         stream outstream = null;
         stream instream = null;
         streamreader sr = null;
         httpwebresponse response = null;
         httpwebrequest request = null;
         encoding encoding = encoding.utf8;
         byte[] data = encoding.getbytes(postdata);
         // 准备请求...
         try
         {
             // 设置参数
             request = webrequest.create(posturl) as httpwebrequest;
             cookiecontainer cookiecontainer = new cookiecontainer();
             request.cookiecontainer = cookiecontainer;
             request.allowautoredirect = true;
             request.method = "post";
             request.contenttype = "application/x-www-form-urlencoded";
             request.contentlength = data.length;
             outstream = request.getrequeststream();
             outstream.write(data, 0, data.length);
             outstream.close();
             //发送请求并获取相应回应数据
             response = request.getresponse() as httpwebresponse;
             //直到request.getresponse()程序才开始向目标网页发送post请求
             instream = response.getresponsestream();
             sr = new streamreader(instream, encoding);
             //返回结果网页（html）代码
             string content = sr.readtoend();
             string err = string.empty;
             return content;
         }
         catch (exception ex)
         {
             string err = ex.message;
             response.write(err);
             return string.empty;
         }
     }