用正则表达式做内容关键字链接

 

 private void rc()
    {
        string str1 = "<img src=\"sss.jpg\" alt=\"网络技术网络;网络应用\">网络技术网络;网络应用 网络基本知识 <img src=\"sss.jpg\" alt=\"网络技术网络;网络应用\"><a  href=\"http://www.stobar.cn/">网络技术网络;网络应用 网络基本知识</a>";

 List<string> keys = new List<string>();
        keys.Add("网络");
        keys.Add("网络技术");
        keys.Add("网络基本");
        string result = keyAddUrl(str1, keys,"http://www.baidu.com/");
        this.Label1.Text = result;

    }

    /// <summary>
    /// 给关键字加链接，同一关键字只加一次
    /// </summary>
    /// <param name="src">源字符串</param>
    /// <param name="keys">关键字泛型</param>
    /// <param name="keys">链接地址</param>
    /// <returns>替换后结果</returns>
    private string keyAddUrl(string src, List<string> keys ,string URL)
    {
        Regex reg = new Regex(@"(?i)(?:^|(?<!<a\b(?>[^<>]*))>)(?>[^<>]*)(?:<|$)");
        int length = 0;
        string temp = string.Empty;
        return reg.Replace(src, delegate(Match m)
        {
            temp = m.Value;
            length = temp.Length;
            for (int i = keys.Count - 1; i >= 0; i--)
            {
                temp = Regex.Replace(temp, @"(?is)^((?:(?:(?!" + Regex.Escape(keys[i]) + @"|</?a\b).)*<a\b(?:(?!</?a\b).)*</a>)*(?:(?!" + Regex.Escape(keys[i]) + @"|</?a\b).)*)(?<tag>" + Regex.Escape(keys[i]) + @")", @"$1<a href="+URL+" target=\"_blank\" title=\"${tag}\">${tag}</a>");
                if (length != temp.Length)
                {
                    keys.Remove(keys[i]);
                }
                length = temp.Length;
            }
            return temp;
        });
    }