asp.net（文章截取前几行作为列表摘要）无损返回HTML代码

代码如下:
<BR>        /* <STRONG>时间很久远了，有码友要，我抄了下来，记得使用的时候还是有部分例外情况要处理，大部分是ok的。</STRONG>
        * 函数： 
        * 说明：无损返回HTML代码
        *      
        * 作者：卡斯Kas(QQ：10590916)
        * 修改：2010-12-13、
        */

        public static string LeftH(string str, int l)
        {
            //为了防止错误
            string odstr = str;
            bool isHtml = false;//判断截取开头是否是字符串
            int maxLen = str.Length;
            int n = 0, i = 0, b = 0, e = 0;
            string c, c2 = "", Start = "", EndLabel = "", AllLabel = "";
            if (l >= str.Length) return str;//截取字段大于字符长度

            bool isErr = false;
            try
            {
            while (n < l && i < maxLen)
            {
                //1
                i++;
                c = str.Substring(i - 1, 1);

                string end2str = "";
                try
                {
                    end2str = str.Substring(i - 1, 2);
                }
                catch
                {
                    end2str = "";
                }
                if (c == "<" && end2str != "</")
                {
                    isHtml = true;
                    b = i;//记录一个位置
                    //5     解决非成对标签

                    string end2tag = "";
                    try
                    {
                        end2tag = str.Substring(i, 2);
                    }
                    catch
                    {
                        end2tag = "";
                    }

                    if (end2tag == "br")
                    {
                        isHtml = false;
                    }
                    if (str.Substring(i, 1).ToLower() == "%")
                    {
                        isHtml = false;
                    }
                    if (str.Substring(i, 1).ToLower() == "?")
                    {
                        isHtml = false;
                    }
                    else if (end2tag == "hr")
                    {
                        isHtml = false;
                    }
                    //5end
                }
                //1end

                //2
                if (c == "<" && end2str == "</")
                {
                    c2 = str.Substring(i - 1, str.Substring(i - 1).IndexOf(">") + 1);
                    AllLabel = AllLabel.Substring(c2.Length);
                }
                //2end

                Start = Start + c;//记录当前字符及其前面字符

                if (!isHtml)
                {
                    //6     较为准确的计数
                    try
                    {
                        if (str.Substring(i, 2).ToLower() == "br")
                        {
                        }
                        else if (str.Substring(i, 2).ToLower() == "hr")
                        {
                        }
                        else
                        {
                            n++;
                        }
                    }
                    catch
                    {
                        //如果出错，则返回纯文本(@"<[^>]+>|</[^>]+>");
                        //odstr = Regex.Replace(odstr, @"<[^>]+>|</[^>]+>", "", RegexOptions.IgnoreCase);
                        odstr = odstr.Replace("<", "<").Replace(">", ">");
                        if (l > odstr.Length) l = odstr.Length;
                        return odstr.Substring(0, l);
                    }
                    //6end
                }
                else
                {
                    if (c == ">")//如果循环到>时，要处理的成对标签中间部分
                    {
                        if (isHtml)
                        {
                            EndLabel = str.Substring(b, i - b);//获取<到>之间的代码
                            e = EndLabel.IndexOf(" ");//标签属性都有空格，以空格为分割，获取标签名
                            if (e > 0)
                            {
                                EndLabel = "</" + EndLabel.Substring(0, e) + ">";
                            }
                            else
                            {
                                EndLabel = "</" + EndLabel;
                            }
                            AllLabel = EndLabel + AllLabel;//记录当前结束标签，及所有有关结束标签
                        }
                        isHtml = false;//重置属性，从新开始
                    }
                }
                //4     当结束时，发现有未闭合的标签，则重新来一次
                if (n + 1 >= l)
                {
                    if (InStrN(Start, "<") != InStrN(Start, ">"))
                    {
                        n--;
                    }
                }
                //4end
            }//end while

            }
            catch
            {
                isErr = true;
            }

            string newReString = Start + AllLabel + "...";

            //最后再次验证
            Regex Rg = new Regex("<.[^>/]+>", RegexOptions.Compiled);
            Regex Rg2 = new Regex(@"<\s*/[a-z]\s*>", RegexOptions.Compiled);

            if (inStrLen(newReString, "<") != inStrLen(newReString, ">"))
            {
                isErr = true;
            }
            else if (inStrLen(newReString.Replace(""", "\""), "\"") % 2 == 1)
            {
                isErr = true;
            }
            else if (Rg.Matches(newReString).Count != Rg2.Matches(newReString).Count)
            {
                isErr = true;
            }
            if (isErr)
            {
                odstr = odstr.Replace("<", "<").Replace(">", ">").Replace("\"", """).Replace("'", "'");
                if (l > odstr.Length)
                { newReString = odstr; }
                else
                {
                    try
                    {
                        newReString = odstr.Substring(0, l) + "...";
                    }
                    catch
                    {
                        newReString = odstr;
                    }
                }
            }

            return newReString;//返回
        }