asp.Net文章の切り取り要約は省略記号で表す

正規簡易版htmlラベル除去

public static string ReplaceHtmlTag(string html, int length = 0)
{
    string strText = System.Text.RegularExpressions.Regex.Replace(html, "<[^>]+>", "");
    strText = System.Text.RegularExpressions.Regex.Replace(strText, "&[^;]+;", "");

    if (length > 0  && strText.Length > length)
        return strText.Substring(0, length);

    return strText;
}

リッチテキストのhtmlラベルをすべて削除してから切り取ります

 #region
        /// <summary>
        ///        html  
        /// </summary>
        /// <param name="htmlstring">   </param>
        /// <returns></returns>
        public  string RemoveHtml(string htmlstring)
        {

            //    

            htmlstring = Regex.Replace(htmlstring, @"<script[^>]*?>.*?</script>", "", RegexOptions.IgnoreCase);

            //  HTML

            htmlstring = Regex.Replace(htmlstring, @"<(.[^>]*)>", "", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"([\r
])[\s]+", "", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"-->", "", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"<!--.*", "", RegexOptions.IgnoreCase);



            htmlstring = Regex.Replace(htmlstring, @"&(quot|#34);", "\"", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"&(amp|#38);", "&", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"&(lt|#60);", "<", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"&(gt|#62);", ">", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"&(nbsp|#160);", " ", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"&(iexcl|#161);", "\xa1", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"&(cent|#162);", "\xa2", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"&(pound|#163);", "\xa3", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"&(copy|#169);", "\xa9", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"&#(\d+);", "", RegexOptions.IgnoreCase);



            htmlstring = htmlstring.Replace("<", "");

            htmlstring= htmlstring.Replace(">", "");

            htmlstring= htmlstring.Replace("\r
", "");

            htmlstring = HttpContext.Current.Server.HtmlEncode(htmlstring).Trim();



            return htmlstring;

        }

        /// <summary>
        ///        
        /// </summary>
        /// <param name="inputString">   </param>
        /// <param name="len">    </param>
        /// <returns></returns>
        public string CutString(string inputString, int len)
        {
            var ascii = new ASCIIEncoding();
            int tempLen = 0;
            string tempString = "";
            byte[] s = ascii.GetBytes(inputString);
            for (int i = 0; i < s.Length; i++)
            {
                if ((int)s[i] == 63)
                {
                    tempLen += 2;
                }
                else
                {
                    tempLen += 1;
                }

                try
                {
                    tempString += inputString.Substring(i, 1);
                }
                catch
                {
                    break;
                }

                if (tempLen > len)
                    break;
            }
            //             
            byte[] mybyte = System.Text.Encoding.Default.GetBytes(inputString);
            if (mybyte.Length > len)
                tempString += "…";


            return tempString;
        }
        #endregion