用Parse會引發例外，用TryParse幫我們把值轉型 成功回傳true，轉型失敗會轉成初始值，並回傳false 不會引發例外
用以下範例示範

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string cdate = "aaaa/a/a/";
            try
            {
                DateTime dt =   DateTime.Parse(cdate);
             }
            catch (Exception ex)
            {
                Console.WriteLine(cdate+ ex.Message.ToString()); 
            }
           
            DateTime trydate; 
            if (DateTime.TryParse(cdate, out trydate))
            {//回傳true
                Console.WriteLine(trydate);
            }
            else {
                Console.WriteLine(trydate + "不正確的日期格式");
            }
 
            Console.ReadKey();
        } 
    }
}