post方法

 CookieContainer cookie = new CookieContainer();
 private string HttpPost(string Url, string postDataStr)
         {
             HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);
             request.Method = "POST";
             request.ContentType = "application/x-www-form-urlencoded";
             request.ContentLength = Encoding.UTF8.GetByteCount(postDataStr);
             request.CookieContainer = cookie;
             Stream myRequestStream = request.GetRequestStream();
             StreamWriter myStreamWriter = new StreamWriter(myRequestStream, Encoding.GetEncoding("gb2312"));
             myStreamWriter.Write(postDataStr);
             myStreamWriter.Close();

             HttpWebResponse response = (HttpWebResponse)request.GetResponse();

             response.Cookies = cookie.GetCookies(response.ResponseUri);
             Stream myResponseStream = response.GetResponseStream();
             StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));
             string retString = myStreamReader.ReadToEnd();
             myStreamReader.Close();
             myResponseStream.Close();

             return retString;
         }

在post的时候有时也用的到cookie，像登录163发邮件时候就需要发送cookie，所以在外部一个cookie属性随时保存 CookieContainer cookie = new CookieContainer();

！注意：有时候请求会重定向，但我们就需要从重定向url获取东西，像QQ登录成功后获取sid，但上面的会自动根据重定向地址跳转。我们可以用:
request.AllowAutoRedirect = false;设置重定向禁用，你就可以从headers的Location属性中获取重定向地址