private string m_Location = "", m_IpAddress = "", m_Response = "";

        /// <summary>
        /// 新建IpLocation实例以获得IP地理位置
        /// </summary>
        /// <param name="ipAddress"></param>
        public IpLocation(string ipAddress)
        {
            m_IpAddress = ipAddress.Trim();

            string[] ip = ipAddress.Split('.');

            ipAddress = ip[0] + "." + ip[1] + ".1.1";

            WebClient client = new WebClient();
            client.Encoding = System.Text.Encoding.GetEncoding("GB2312");

            string url = "http://www.ip138.com/ips.asp";
            string post = "ip=" + ipAddress + "&action=2";
            client.Headers.Set("Content-Type", "application/x-www-form-urlencoded");         //尤其是这一句
            string response = client.UploadString(url, post);                                 //这里
            m_Response = response;                                                               

            string p = @"<li>参考数据二：(?<location>[^<>]+?)</li>";                         //和这一句

            Match match = Regex.Match(response, p);                                           //还有这里
            m_Location = match.Groups["location"].Value.Trim();                                 //和这里
        }

        /// <summary>
        /// 返回Ip地址的地理位置名称
        /// </summary>
        public string Location
        {
            get
            {
                return m_Location;
            }
        }

        public string IpAddress
        {
            get
            {
                return m_IpAddress;
            }
        }

        /// <summary>
        /// 返回网络反馈原始数据
        /// </summary>
        public string Response
        {
            get
            {
                return m_Response;
            }
        }

// 指定表单向服务器提交的编码类型,默认就上这个
            client.Headers.Set("Content-Type", "application/x-www-form-urlencoded");         //尤其是这一句

            // 向"http://www.ip138.com/ips.asp";页面post数据
            string response = client.UploadString(url, post);                                 //这里
            m_Response = response;

            // 用于解析结果的正则表达式
            string p = @"<li>参考数据二：(?<location>[^<>]+?)</li>";                         //和这一句

            // 正则解析网页的返回内容
            Match match = Regex.Match(response, p);                                           //还有这里
            
            // 取出匹配内容
            m_Location = match.Groups["location"].Value.Trim();                                 //和这里