.NET截取指定長度漢字超出部分以...代替

///   <summary>    
///   將指定字符串按指定長度進行剪切，    
///   </summary>    
///   <param   name= "oldStr "> 需要截斷的字符串 </param>    
///   <param   name= "maxLength "> 字符串的最大長度 </param>    
///   <param   name= "endWith "> 超過長度的後綴 </param>    
///   <returns> 如果超過長度，返回截斷後的新字符串加上後綴，否則，返回原字符串</returns>    
   public static string StringTruncat(string oldStr, int maxLength, string endWith)   
   {   
       if (string.IsNullOrEmpty(oldStr))   
          //   throw   new   NullReferenceException( "原字符串不能爲空 ");    
           return oldStr + endWith;   
       if (maxLength < 1)   
           throw new Exception("返回的字符串長度必須大於[0] ");   
       if (oldStr.Length > maxLength)   
       {   
           string strTmp = oldStr.Substring(0, maxLength);   
           if (string.IsNullOrEmpty(endWith))   
              return strTmp;   
           else  
               return strTmp + endWith;   
       }   
       return oldStr;   
   }