html转换为纯文本,支持撇号

 /// <summary>

        /// html转换为纯文本

        /// </summary>

        /// <param name="source"></param>

        /// <returns></returns>

        private static string HtmlToPlainText(string source)

        {

            string result;

            //remove line breaks,tabs

            result = source.Replace("\r", " ");

            result = result.Replace("\n", " ");

            result = result.Replace("\t", " ");

            //remove the header

            result = Regex.Replace(result, "(<head>).*(</head>)", string.Empty, RegexOptions.IgnoreCase);

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

            result = Regex.Replace(result, @"(<script>).*(</script>)", string.Empty, RegexOptions.IgnoreCase);

            //remove all styles

            result = Regex.Replace(result, @"<( )*style([^>])*>", "<style>", RegexOptions.IgnoreCase); //clearing attributes

            result = Regex.Replace(result, "(<style>).*(</style>)", string.Empty, RegexOptions.IgnoreCase);

            //insert tabs in spaces of <td> tags

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

            //insert line breaks in places of <br> and <li> tags

            result = Regex.Replace(result, @"<( )*br( )*>", "\r", RegexOptions.IgnoreCase);

            result = Regex.Replace(result, @"<( )*li( )*>", "\r", RegexOptions.IgnoreCase);

            //insert line paragraphs in places of <tr> and <p> tags

            result = Regex.Replace(result, @"<( )*tr([^>])*>", "\r\r", RegexOptions.IgnoreCase);

            result = Regex.Replace(result, @"<( )*p([^>])*>", "\r\r", RegexOptions.IgnoreCase);

            //remove anything thats enclosed inside < >

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

            //replace special characters:

            result = Regex.Replace(result, @"&amp;", "&", RegexOptions.IgnoreCase);

            result = Regex.Replace(result, @"&nbsp;", " ", RegexOptions.IgnoreCase);

            result = Regex.Replace(result, @"&lt;", "<", RegexOptions.IgnoreCase);

            result = Regex.Replace(result, @"&gt;", ">", RegexOptions.IgnoreCase);

            result = Regex.Replace(result, @"'", "'", RegexOptions.IgnoreCase);

            result = Regex.Replace(result, @"&(.{2,6});", string.Empty, RegexOptions.IgnoreCase);

            //remove extra line breaks and tabs

            result = Regex.Replace(result, @" ( )+", " ");

            result = Regex.Replace(result, "(\r)( )+(\r)", "\r\r");

            result = Regex.Replace(result, @"(\r\r)+", "\r\n");

            return result;

        }