/// <summary>

        /// 向某个url提交数据并读取该地址返回的xml,并将xml转换成dataset,并返回dataset中某个表

        /// </summary>

        /// <param name="url">提交的低至</param>

        /// <param name="param">参数</param>

        /// <param name="tableName">表名</param>

        /// <param name="encoding">编码格式</param>

        /// <returns></returns>

        public static DataSet PostData(string url, string param, String tableName, Encoding encoding)

        {
           #region post数据

            DataSet ds = new DataSet(); DataTable dt = new DataTable();

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

            req.Timeout = ;

            try

            {

                byte[] requestbytes = encoding.GetBytes(param);

                req.Method = "post";

                req.ContentType = "application/x-www-form-urlencoded";

                req.ContentLength = requestbytes.Length;

                System.IO.Stream requeststream = req.GetRequestStream();

                requeststream.Write(requestbytes, , requestbytes.Length);

                requeststream.Close();

                HttpWebResponse res = (HttpWebResponse)req.GetResponse();

                System.IO.StreamReader sr = new System.IO.StreamReader(res.GetResponseStream(), encoding);

                String backstr = sr.ReadToEnd();

                StringReader txtReader = new StringReader(backstr);

                XmlTextReader xmlReader = new XmlTextReader(txtReader);

                ds.ReadXml(xmlReader);

                sr.Close();

                res.Close();

                sr.Dispose();

            }

            catch

            {

                return null;

            }

            //条件判断

            //if (ds != null && ds.Tables.Count > 0 && ds.Tables[tableName] != null)

            //{

            //    dt = ds.Tables[tableName].Copy();

            //}

            if (ds != null && ds.Tables.Count > )

            {

                //  dt = ds.Tables[tableName].Copy();

                return ds;

            }

            return ds;

            #endregion

        }

                string url = Config.PassportUserInfoUrl + "&userid=" + userid;//可以把链接放到配置文件中

                string result = SlRequest.GetResponse(url, "");

                XmlDocument doc = new XmlDocument();

                doc.LoadXml(result);

                XmlNode node = doc.SelectSingleNode("soufun_passport/common");//选择XML节点的值

                if (node != null)

                {

                    string resMsg = node.SelectSingleNode("return_result").InnerText;

                    if (resMsg == "")

                    {

                       //此处可以定义一个User实体类, 来接收关于User的Inforeturn user;

                    }

                    else

                    {

                        errorMessage = node.SelectSingleNode("error_reason").InnerText;

                        return null;

                    } 
                //此处讲判断某个XML节点下面有几个子节点

if (node.ChildNodes.Count > 3)
                   {
                        resMsg = "";
                    }

       /// 将XmlDocument转化为string

       /// </summary>

       /// <param name="xmlDoc"></param>

       /// <returns></returns>

       public string ConvertXmlToString(XmlDocument xmlDoc)

       {

           MemoryStream stream = new MemoryStream();

           XmlTextWriter writer = new XmlTextWriter(stream, null);

           writer.Formatting = Formatting.Indented;

           xmlDoc.Save(writer);

    StreamReader sr = new StreamReader(stream, System.Text.Encoding.UTF8);

           stream.Position = ;

           string xmlString = sr.ReadToEnd();

           sr.Close();

           stream.Close();

    return xmlString;

       }