抓取网页，过滤得到全部UR地址，如何写

        //采集测试        protected void btnCrawltest_Click(object sender, EventArgs e)        {            btnCrawltest.Enabled = false;            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(txtTargeturl.Text);            HttpWebResponse response = (HttpWebResponse)request.GetResponse();            StreamReader sr = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding(myHelper.getEncode(txtTargeturl.Text)));                       //绑定链接列表51aspx.com            repeaterLinks.DataSource = getLinks(txtKeyurl.Text, sr.ReadToEnd(), txtTargeturl.Text);            repeaterLinks.DataBind();            sr.Close();            btnCrawltest.Enabled = true;            Utility.Msg.Show(this,"采集测试完成！");        }        /// <summary>        /// 51aspx.com获取页面中的链接列表        /// </summary>        /// <param name="keyurl">链接标记</param>        /// <param name="inStr">代码内容</param>        /// <param name="targeturl">目标网址</param>        /// <returns>链接列表51aspx.com</returns>        private DataSet getLinks(string keyurl, string inStr, string targeturl)        {            string strLink = @"(?:<a[\s\S]*?href=['""]?(?<url>[^'""> ]+)['""]?[^>]+>(?<title>[\s\S]*?)</a>)";            return myHelper.getResult(inStr, strLink, keyurl, targeturl, "", "");        }        protected void Button1_Click(object sender, EventArgs e)        {            lbHtml.Text = "1223345455";        }