/// <summary>
    /// 删除标签
    /// </summary>
    /// <param name="tags"></param>
    /// <param name="tag"></param>
    private static void RemoveTag(List<string> tags, string tag)
    {
        for (int i = tags.Count - 1; i >= 0; i--) if (tags[i].IndexOf(tag) == 1) { tags.RemoveAt(i); break; }
    }
    /// <summary>
    /// 按文本内容长度截取HTML字符串(支持截取带HTML代码样式的字符串)
    /// </summary>
    /// <param name="html">将要截取的字符串参数</param>
    /// <param name="len">截取的字节长度</param>
    /// <param name="endString">字符串末尾补上的字符串</param>
    /// <returns>返回截取后的字符串</returns>
    public static string HTMLSubstring(string html, int len, string endString)
    {
        if (string.IsNullOrEmpty(html) || html.Length <= len) return html;
        MatchCollection mcentiry, mchtmlTag;
        List<string> inputHTMLTag = new List<string>();
        string r = "", tmpValue, nowtag, losetag;
        int rWordCount = 0, wordNum = 0, i = 0;
        Regex rxSingle = new Regex("^<(br|hr|img|input|param|meta|link|wbr)", RegexOptions.Compiled | RegexOptions.IgnoreCase)//是否单标签正则
            , rxEndTag = new Regex("</[^>]+>", RegexOptions.Compiled)//是否结束标签正则
            , rxTagName = new Regex("</?([a-z\\d]+)[^>]*>", RegexOptions.Compiled | RegexOptions.IgnoreCase)//获取标签名正则
            , rxHtmlTag = new Regex("<[^>]+>", RegexOptions.Compiled)//html标签正则
            , rxEntity = new Regex("&[a-z]{1,9};", RegexOptions.Compiled | RegexOptions.IgnoreCase)//实体正则
            , rxEntityReverse = new Regex("§", RegexOptions.Compiled)//反向替换实体正则
            ;
        html = html.Replace("§", "&#167;");//替换字符§为他的实体“&#167;”，以便进行下一步替换
        mcentiry = rxEntity.Matches(html);//收集实体对象到匹配数组中
        html = rxEntity.Replace(html, "§");//替换实体为特殊字符§，这样好控制一个实体占用一个字符
        mchtmlTag = rxHtmlTag.Matches(html);//收集html标签到匹配数组中

        string[] arrWord = rxHtmlTag.Split(html);//拆分
        wordNum = arrWord.Length;


        //获取指定内容长度及HTML标签
        for (; i < wordNum; i++)
        {
            if (rWordCount + arrWord[i].Length >= len) r += arrWord[i].Substring(0, len - rWordCount) + endString;
            else r += arrWord[i];


            rWordCount += arrWord[i].Length;//计算已经获取到的字符长度

            if (rWordCount >= len) break;

            //搜集已经添加的非单标签，以便封闭HTML标签对
            if (i < wordNum - 1)
            {
                tmpValue = mchtmlTag[i].Value.ToLower(); 
                if (!rxSingle.IsMatch(tmpValue))
                { //不是单标签
                    if (rxEndTag.IsMatch(tmpValue) && inputHTMLTag.Count > 0)
                    {//这里注意区分结束标签是否和最近一次加入的标签匹配
                        nowtag = rxTagName.Match(tmpValue).Groups[1].Value.ToLower();
                        losetag = rxTagName.Match(inputHTMLTag[inputHTMLTag.Count - 1]).Groups[1].Value.ToLower();
                        inputHTMLTag.RemoveAt(inputHTMLTag.Count - 1);
                        if (nowtag != losetag)
                        {
                            RemoveTag(inputHTMLTag, nowtag);
                            r += "</" + losetag + ">";//补全丢失的标签
                        }
                    }
                    else inputHTMLTag.Add(tmpValue);
                }
                r += tmpValue;
            }
        }
        //替换回实体
        for (i = 0; i < mcentiry.Count; i++) r = rxEntityReverse.Replace(r, mcentiry[i].Value, 1);
        //封闭标签
        for (i = inputHTMLTag.Count - 1; i >= 0; i--) r += "</" + rxTagName.Match(inputHTMLTag[i].ToString()).Groups[1].Value + ">";
        return r;
    }