/// <summary>

         /// 截断字符串

         /// </summary>

         /// <param name="s">要截断的字符串</param>

         /// <param name="len">要保留的字符长度</param>

         /// <returns>截断后的字符串</returns>

         public static string Format(string s, int len)

         {

             if (s.Length > len)

                 s = s.Substring(, len) + "...";

             return s;

         }