/// <summary>
        /// 交易
        /// </summary>
        public void Dealing()
        {
            Console.WriteLine("Welcom! We got Nokia, Lenovo and Apple, what do you like?");
            string input = Console.ReadLine();

            Console.WriteLine("how many {0} do you want?", input);
            int quantity = Convert.ToInt32(Console.ReadLine());

            Goods[] goods       = repository.GetGoods(input, quantity);
            double  totalAmount = goods[0].Price * goods.Length;//打折前总价

            Console.WriteLine("select discounting type: 1--no discount  2--10% off   3--15% off 4--up to 500 reduce 100");
            DiscountBase discoun = GetDiscountType(Console.ReadLine());

            //打印小票
            foreach (Goods item in goods)
            {
                Console.WriteLine("item: {0}\tID: {2}\tprice: {1} Yuan", item.Name, item.Price, item.ID);
            }
            Console.WriteLine("total: {0} Yuan\npayment: {1} Yuan", goods[0].Price * goods.Length, discoun.GetDiscountedAmount(totalAmount));
        }
        /// <summary>
        /// 简单工厂模式,根据选择的打折方式返回打折对象
        /// </summary>
        /// <param name="input">输入的数字</param>
        /// <returns>打折的父类,装的是子类对象</returns>
        public DiscountBase GetDiscountType(string input)
        {
            DiscountBase dis = null;

            switch (input)
            {
            case "1":
                dis = new NoDiscount();
                break;

            case "2":
                dis = new DisountByRate(0.9);
                break;

            case "3":
                dis = new DisountByRate(0.85);
                break;

            case "4":
                dis = new UpTo_Discount(500, 100);
                break;
            }
            return(dis);
        }