.NET截取指定长度汉字超出部分以"..."代替

Code
/// <summary>
/// 将指定字符串按指定的长度进行剪切
/// </summary>
/// <param name="oldStr">需要裁剪的字符串</param>
/// <param name="maxLength">字符串的最大长度</param>
/// <param name="endWith">超过长度的后缀</param>
/// <returns>如果超过长度，返回截断后的新字符串加上后缀，否则，返回原字符串</returns>
public static string StringTruncat(string oldStr, int maxLength, string endWith)
{
if (string.IsNullOrEmpty(oldStr))
{
//throw new NullReferenceException(" 原字符串不能为空 ");
return oldStr + endWith;
}
if (maxLength < 1)
{
throw new Exception(" 返回字符串的长度必须大于[0] ");
}

if (oldStr.Length > maxLength)
{
string tmpStr = oldStr.Substring(0, maxLength);
if (string.IsNullOrEmpty(endWith))
{
return tmpStr;
}
else
{
return tmpStr + endWith;
}
}
return oldStr;
}