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 
        }