///   <summary>   
///   将指定字符串按指定长度进行剪切，   
///   </summary>   
///   <param   name= "Str "> 需要截断的字符串 </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 strTmp;
            else
                return strTmp + endWith;
        }
        return oldStr;
    }