C#中的字符串截取

///<summary>
    ///功能:精確的按要求截取指定長度的字符串
    ///中文算2個英文算一個
    ///參數:str 待截取字符,len 截取長度 symbol 表示字符(....)
    ///</summary>
    public static string GotTopic(string str,int len,string symbol)
    {
        int count = 0;
        string strTemp = "";
        str = NoHtml(str);
        for (int i = 0; i < str.Length; i++)
        {
            if (Math.Abs(((int)(str.Substring(i, 1).ToCharArray())[0])) > 255)
            {
                count += 2;
            }else
            {
                count += 1;
            }
            if (count <= len)
            {
                strTemp += str.Substring(i, 1);
            }
            else
            {
                return strTemp + symbol;
            }

        }
        return str;
    }
    /// <summary>
    /// 過濾掉Html標簽
    /// </summary>
    /// <param name="str"></param>
    /// <returns></returns>
    public static string NoHtml(string str)
    {
        str = Regex.Replace(str, @"(\<.[^\<]*\>)", " ", RegexOptions.IgnorePatternWhitespace | RegexOptions.IgnoreCase);
        str = Regex.Replace(str, @"(\<\/[^\<]*\>)"," ", RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace);
        return str;
       
    }