上码：

string[] imgtag = { ".gif",".jpg",".png",".jpeg" };
            string tpllink = "<a target=\"_blank\" style=\"color:#e25252;text-decoration: underline;\" href='{0}'>{1}</a>";
            Regex re = new Regex(@"((http|https)://)?(([a-zA-Z0-9\._-]+\.[a-zA-Z]{2,6})|([0-9]{1,3}\.[0-9]{1,3}))(:[0-9]{1,4})*(/[^<|^>]*)?");
            MatchCollection matchCollection = re.Matches(txtmsg);
            HashSet<string> urlKeys = new HashSet<string>();
            foreach (Match m in matchCollection)
            {
                if (imgtag.Any(x => m.Value.Contains(x)))
                {
                    continue;
                }

                if (urlKeys.Add(m.Value))
                {
                    txtmsg = txtmsg.Replace(m.Value,String.Format(tpllink,m.Value.Contains("http://") ? m.Value : "http://" + m.Value,m.Value));
                }
            }