.NET截取指定长度的汉字超出部分用“···”代替

/// <summary>
/// 将指定的字符串按指定的长度剪切
/// </summary>
/// <param name="oldStr">需要剪切的字符串</param>
/// <param name="maxLength">需要字符串的最大的长度</param>
/// <param name="endWith">超过长度的后缀</param>
/// <returns>如果超过长度，返回截取的字符串加上后缀；否则返回原字符串</returns>
    public static string StringTruncate(string oldStr, int maxLength, string endWith)
    {
        if (string.IsNullOrEmpty(oldStr))
            return oldStr + endWith;
        if (maxLength < 1)
            throw new Exception("返回的字符串长度必须大于[0]");
        if (oldStr.Length > maxLength)
        {
            string strTmp = oldStr.Substring(0, maxLength);
            if (string.IsNullOrEmpty(endWith))
                return oldStr;
            else
                return  strTmp + endWith;
        }
        return oldStr;
    }
}