[DP] 策略模式

了解策略模式時，發現這段 Youtube 教學影片，是利用折扣來說明，那就拿折扣來練習。

ShoppingMall - Mall Class

namespace ShoppingMall
{
    public class Mall
    {
        public string MallName { get; set; }
        public IDiscount DiscountBehavor { get; set; }

        public decimal calPrice(decimal BillTotal)
        {
            return DiscountBehavor.Discount(BillTotal);
        }
    }

    public class Disc50 : IDiscount
    {
        public decimal Discount(decimal BillTotal)
        {
            return Math.Round(BillTotal * 5 / 10, 0, MidpointRounding.AwayFromZero);
        }

        public string Descript
        {
            get { return "5 折"; }
        }
    }

    public class Disc88 :IDiscount
    {
        public decimal Discount(decimal BillTotal)
        {
            return Math.Round(BillTotal * 88 / 100, 0, MidpointRounding.AwayFromZero);
        }

        public string Descript
        {
            get { return "88 折"; }
        }
    }

    public class Coupon1000 : IDiscount
    {
        public string Descript
        {
            get { return "買萬送千"; }
        }

        public decimal Discount(decimal BillTotal)
        {
            if (BillTotal > 10000)
            BillTotal -= 1000;
            return BillTotal;
        }
    }

    public interface IDiscount
    {
        string Descript { get; }
        decimal Discount(decimal BillTotal);
    }
}

ShoppingMallDemo - Web.Config

<configuration>
  <system.web>
    <compilation debug="true" targetFramework="4.5" />
    <httpRuntime targetFramework="4.5" />
  </system.web>
  <appSettings>
    <add key="discount" value="ShoppingMall.Coupon1000,ShoppingMall"/>
  </appSettings>
</configuration>

ShoppingMallDemo - cs 檔

using ShoppingMall;

public partial class _Default : System.Web.UI.Page
{
    protected void btnCal_Click(object sender, EventArgs e)
    {

        Mall mall = new Mall();
        IDiscount disc = GetDiscount();
        mall.DiscountBehavor = disc;

        lblPay.Text = mall.calPrice(Convert.ToDecimal(txtBillTotal.Text)).ToString();
        lblDisc.Text = disc.Descript;
    }

    IDiscount GetDiscount()
    {
        string setting = System.Configuration.ConfigurationManager.AppSettings["discount"];
        string[] arr = setting.Split(',');
        string dllName = arr[1];
        string className = arr[0];
        IDiscount disc = (IDiscount)System.Reflection.Assembly.Load(dllName).CreateInstance(className);

        return disc;
    }
}

參考資料
• Design pattern :- What is Strategy pattern ?