asp.net清除html标记

#region 清除文本样式  主要应用于从网络粘贴进来的文本
        [WebMethod]
        public static string ClearStyle(string yourStr)//清除样式
        {
            ImageUrl = null;
            string OldString = yourStr;
            StringBuilder UpdateString = new StringBuilder();
            Regex reg = new Regex(@"(?i)<img[^>]*?\s*src=(['""]?)(?<src>[^'""\s>]+)\1[^>]*>");//匹配出img标记
            MatchCollection mc = reg.Matches(yourStr);
            int imgsum = mc.Count;
            ImageUrl = new string[imgsum];
            if (imgsum > 0)
            {
                for (int i = 0; i < imgsum; i++)
                {
                    int len = mc[i].Length;
                    int index = OldString.IndexOf(mc[i].ToString());
                    string indextext = OldString.Substring(0, index);
                &nbs