ASP.NETで文字列を切り取る方法

   ///   
                 

    ///   
    ///    
    ///              
    ///              
    ///             
    ///          ，              ，  ，        
    public static string StringTruncat(string oldStr, int maxLength, string endWith)
    {
        if (string.IsNullOrEmpty(oldStr))
            //   throw   new   NullReferenceException( "         "); 
            return oldStr + endWith;
        if (maxLength < 1)
            throw new Exception("            [0] ");
        if (oldStr.Length > maxLength)
        {
            string strTmp = oldStr.Substring(0, maxLength);
            if (string.IsNullOrEmpty(endWith))
                return strTmp;
            else
                return strTmp + endWith;
        }
        return oldStr;
    }