添加引用：

using System.Web.Script.Serialization;
using System.Collections.Generic;
using Jayrock.Json;

 public void GetInfos()     {        

var code = Request.QueryString["code"];        

string json = string.Empty;        

string url = "https://api.weixin.qq.com/sns/oauth2/access_token?appid=" + appid + "&secret=" + secret + "&code=" + code + "&grant_type=authorization_code";        

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);        

request.Method = "POST";        

using (WebResponse response2 = request.GetResponse())        

{            

using (StreamReader reader = new StreamReader(response2.GetResponseStream(), Encoding.UTF8))            

{                

//得到url返回的数据                

json = reader.ReadToEnd();            

}        

}         //下面可以解析了

        if (!string.IsNullOrEmpty(json))        

{            

//需要添加引用System.Web.Extensions

            //然后还要添加using System.Web.Script.Serialization;

            JavaScriptSerializer jss = new JavaScriptSerializer();

            Dictionary<string, string> dic = jss.Deserialize<Dictionary<string, string>>(json);                        

string[] js = json.Replace("{", "").Replace("}", "").Split(‘,‘);            

token = js[0].ToString().Split(‘:‘)[1].ToString().Substring(1, js[0].ToString().Split(‘:‘)[1].ToString().Length-2);            

openid = js[3].ToString().Split(‘:‘)[1].ToString().Substring(1, js[3].ToString().Split(‘:‘)[1].ToString().Length-2);        

}    

}

调用微信接口取数据