截取指定长度html内容，并保留html格式标记

/// <summary>
    /// 按字节长度截取字符串(支持截取带HTML代码样式的字符串)
    /// </summary>
    /// <param name=”param”>将要截取的字符串参数</param>
    /// <param name=”length”>截取的字节长度</param>
    /// <param name=”end”>字符串末尾补上的字符串</param>
    /// <returns>返回截取后的字符串</returns>
    public string SubstringToHTML(string param, int length, string end)
    {
        string Pattern = null;
        MatchCollection m = null;
        StringBuilder result = new StringBuilder();
        int n = 0;
        char temp;
        bool isCode = false; //是不是HTML代码
        bool isHTML = false; //是不是HTML特殊字符,如&nbsp;
        char[] pchar = param.ToCharArray();
        for (int i = 0; i < pchar.Length; i++)
        {
            temp = pchar[i];
            if (temp == ‘<’)
            {
                isCode = true;
            }
            else if (temp == ‘&’)
            {
                isHTML = true;
            }
            else if (temp == ‘>’ && isCode)
            {
                n = n – 1;
                isCode = false;
            }
            else if (temp == ‘;’ && isHTML)
            {
                isHTML = false;
            }

            if (!isCode && !isHTML)
            {
                n = n + 1;
                //UNICODE码字符占两个字节
                if (System.Text.Encoding.Default.GetBytes(temp + “”).Length > 1)
                {
                    n = n + 1;
                }
            }

            result.Append(temp);
            if (n >= length)
            {
                break;
            }
        }
        result.Append(end);
        //取出截取字符串中的HTML标记
        string temp_result = result.ToString().Replace(“(>)[^<>]*(<?)”, “$1$2″);
        //去掉不需要结素标记的HTML标记
        temp_result = temp_result.Replace(@”</?(AREA|BASE|BASEFONT|BODY|BR|COL|COLGROUP|DD|DT|FRAME|HEAD|HR|HTML

|IMG|INPUT|ISINDEX|LI|LINK|META|OPTION|P|PARAM|TBODY|TD|TFOOT|TH|THEAD

|TR|area|base|basefont|body|br|col|colgroup|dd|dt|frame|head|hr|html|img|input|isindex|li|link|meta

|option|p|param|tbody|td|tfoot|th|thead|tr)[^<>]*/?>”,
         “”);
        //去掉成对的HTML标记
        temp_result = temp_result.Replace(@”<([a-zA-Z]+)[^<>]*>(.*?)</1>”, “$2″);
        //用正则表达式取出标记
        Pattern = (“<([a-zA-Z]+)[^<>]*>”);
        m = Regex.Matches(temp_result, Pattern);
        ArrayList endHTML = new ArrayList();
        foreach (Match mt in m)
        {
            endHTML.Add(mt.Result(“$1″));
        }
        //补全不成对的HTML标记
        for (int i = endHTML.Count – 1; i >= 0; i–)
        {
            result.Append(“</”);
            result.Append(endHTML[i]);
            result.Append(“>”);
        }
        return result.ToString();
    }