C# TryXXXX模式

   public static int? TrayParse(string text) {
             int ret;
             if (int.TryParse(text,out ret)) {
                 return ret;
             }
             else {
                 return null;
             }
         }

static void Main(string []argd){

 int? parsed = TrayParse("Not Valid");
            if (parsed.HasValue) {
                Console.WriteLine("Parsed to {0}",parsed.Value);
            }
            else {
                Console.WriteLine("Couldn't parse");
            }
}