/// <summary>
/// 将指定字符串按指定长度进行剪切
/// </summary>
/// <param name="oldStr">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;
}