C#发送HttpPost请求来调用WebService的方法

void UpdateContactSign()
        {
           string ServerPage ="http://localhost/WebService/MyService.asmx";
            try
            {
                //ServerPage += "?op=TangramAction";
                ServerPage += "/MyAction";//MyAction是WebService中的方法
           string strXml="<a ObjID=\"9\"></a>",;//第一个参数
           string strData="ContactSign|990011|我的数据";//第二个参数
           string res = HttpConnectToServer(ServerPage, strXml, strData);
                //MessageBox.Show(res);
            }
            catch (Exception ex)
            {

            }
        }

        //发送消息到服务器
      public string HttpConnectToServer(string ServerPage,string strXml,string strData)
        {
            string postData = "strXml=" + strXml+"&strData="+strData;

            byte[] dataArray = Encoding.Default.GetBytes(postData);
            //创建请求
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(ServerPage);
            request.Method = "POST";
            request.ContentLength = dataArray.Length;
            request.ContentType = "application/x-www-form-urlencoded";
            //创建输入流
            Stream dataStream = null;
            try
            {
                dataStream = request.GetRequestStream();
            }
            catch (Exception)
            {
                return null;//连接服务器失败
            }

            //发送请求
            dataStream.Write(dataArray, 0, dataArray.Length);
            dataStream.Close();
            //读取返回消息
            string res = string.Empty;
            try
            {
                HttpWebResponse response = (HttpWebResponse)request.GetResponse();
                StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.UTF8);
                res = reader.ReadToEnd();
                reader.Close();
            }
            catch (Exception ex)
            {
                return null;//连接服务器失败
            }
            return res;
        }