.Net实战之反射外卖计费

场景

叫外卖支付，可以有以下优惠：

1、满30元减12

2、是会员减配送费，比如5元

3、优惠券

….

问题? 如何在不改代码的情况下更灵活的去控制优惠的变化？？？

有些代码与实际业务可能不符合，旨在体验反射的用处

   public interface IDiscount
    {
        /// <summary>
        /// 优惠名称
        /// </summary>
        string Name { get; }
        
        /// <summary>
        /// 金额
        /// </summary>
        /// <param name="money"></param>
        /// <returns></returns>
        double CalcMoney(double totalMoney);
    }

--代金券

namespace CashLib
{
    /// <summary>
    /// 代金券
    /// </summary>
    public class CashDiscount:IDiscount
    {
        public string Name
        {
            get { return "代金券:兔子粮票2元，可抵扣2元"; }
        }

        public double CalcMoney(double totalMoney)
        {
            return totalMoney - 2;
        }
    }
}

--会员

namespace MembeLib
{
    /// <summary>
    /// 会员
    /// </summary>
    public class MemberDiscount:IDiscount
    { 
        public string Name
        {
            get { return "会员免5元配送费"; }
        }

        public double CalcMoney(double totalMoney)
        {
            return totalMoney - 5;
        }
    }
}

--满金额减免

namespace MinusLib
{
    /// <summary>
    /// 足价减金额
    /// </summary>
    public class MinusDiscount : IDiscount
    {
        public string Name
        {
            get { return "满30减12元"; }
        }

        public double CalcMoney(double totalMoney)
        {
            return totalMoney - 12;
        }
    }
}

--读取优惠策略的程序集，动态创建类的对象并调用类的成员

    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }


        Dictionary<string, object> dict = new Dictionary<string, object>();
        private void Form1_Load(object sender, EventArgs e)
        {
            string dllPath = AppDomain.CurrentDomain.BaseDirectory + "DiscountLib/";
            string[] assFiles = System.IO.Directory.GetFiles(dllPath, "*.dll");
            foreach (var dllItem in assFiles)
            {
                Assembly ass = Assembly.LoadFrom(dllItem);

                foreach (Type type in ass.GetTypes())
                {
                    if (typeof(IDiscount).IsAssignableFrom(type))
                    {
                        object instanceDiscount = ass.CreateInstance(type.FullName);
                        PropertyInfo propDiscountName = type.GetProperty("Name");
                        string discountName = propDiscountName.GetValue(instanceDiscount).ToString();

                        this.listBox1.Items.Add(discountName);
                        dict.Add(discountName, instanceDiscount);

                    }
                }
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            CustomerOrder cusOrder = new CustomerOrder("张三", 35);
            foreach (string item in this.listBox1.SelectedItems)
            {
                cusOrder.AddDiscount(dict[item] as IDiscount);
            }
            cusOrder.UseDiscount();
        }


    }