读《大话设计模式》——应用工厂模式的"商场收银系统"(WinForm)

　　要做的是一个商场收银软件，营业员根据客户购买商品单价和数量，向客户收费。两个文本框，输入单价和数量，再用个列表框来记录商品的合计，最终用一个按钮来算出总额就可以了，还需要一个重置按钮来重新开始。

　　

　　核心代码(v1.0)

 //声明一个double变量total来计算总计
        double total = 0.0d;
        private void btnConfirm_Click(object sender, EventArgs e)
        {
            //声明一个double变量totalPrices来计算每个商品的单价(txtPrice) * 数量(txtNum)后的合计
            double totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text);
            //将每个商品合计计入总计
            total = total + totalPrices;
            //在列表框中显示信息
            lbxList.Items.Add("单价:" + txtPrice.Text + "  数量:" + txtNum.Text + "  合计:" + totalPrices.ToString());
            //在lblTotalShow标签上显示总计数
            lblTotalShow.Text = total.ToString();
        }

　　需求又来了，现在要求商场对商品搞活动，所有的商品打 8 折。扩展功能加了一个下拉选择框……v1.1版本来了

　　核心代码(v1.1)

namespace ExtendDiscount
{
    public partial class frmMain :Skin_Metro
    {
        public frmMain()
        {
            InitializeComponent();
        }
        //声明一个double变量total来计算总计
        double total = 0.0d;
        private void btnConfirm_Click(object sender, EventArgs e)
        {
            //声明一个double变量totalPrices
            double totalPrices = 0d;
            //加入打折情况
            switch (cbxType.SelectedIndex)
            {
                case :
                    totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text);
                    break;
                case :
                    totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text) * 0.8;
                    break;
                case :
                    totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text) * 0.7;
                    break;
                case :
                    totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text) * 0.5;
                    break;
            }
            //将每个商品合计计入总计
            total = total + totalPrices;
            //在列表框中显示信息
            lbxList.Items.Add("单价:" + txtPrice.Text + "  数量:" + txtNum.Text + "  合计:" + totalPrices.ToString());
            //在lblTotalShow标签上显示总计数
            lblTotalShow.Text = total.ToString();
        }

        private void frmMain_Load(object sender, EventArgs e)
        {
            cbxType.SelectedIndex = ;
        }

        private void txtPrice_KeyPress(object sender, KeyPressEventArgs e)
        {
            //数字0~9所对应的keychar为48~57
            e.Handled = true;
            //输入0-9
            if ((e.KeyChar >=  && e.KeyChar <= ) || e.KeyChar == )
            {
                e.Handled = false;
            }
        }

        private void txtNum_KeyPress(object sender, KeyPressEventArgs e)
        {
            //数字0~9所对应的keychar为48~57
            e.Handled = true;
            //输入0-9
            if ((e.KeyChar >=  && e.KeyChar <= ) || e.KeyChar == )
            {
                e.Handled = false;
            }
        }

        private void btnReset_Click(object sender, EventArgs e)
        {
            total = 0.0;
            txtPrice.Text = "";
            txtNum.Text = "";
            lblTotalShow.Text = "";
            lbxList.Items.Clear();
            cbxType.SelectedIndex = ;
        }
    }
}

　　简单的工厂模式在WinForm中的应用

　　现在又根据市场情况，添加此类需求——“满300送100、满200送50等等“

　　面向对象的编程，并不是类越多越好，类的划分是为了封装，但分类的基础是抽象，具有相同属性和功能的对象的抽象集合才是类，打一折和打九折只是形式的不同，抽象分析出来，所有的打折算法都是一样的，所以打折算法应该是一个类；而”满300送100“等等，返利算法应该是另一个类。

　　

　　代码(v1.2)

　　

namespace ExtendDiscountOfSimpleFactoryPattern
{
    //现金收取父类
    abstract class CashSuper
    {
        //抽象方法:收取现金，参数为原价，返回为当前价
        public abstract double acceptCash(double money);
    }
}

namespace ExtendDiscountOfSimpleFactoryPattern
{
    //正常消费，继承CashSuper
    class CashNormal:CashSuper
    {
        public override double acceptCash(double money)
        {
            return money;
        }
    }
}

namespace ExtendDiscountOfSimpleFactoryPattern
{
    //打折收费消费，继承CashSuper
    class CashRebate:CashSuper
    {
        private double moneyRebate = 1d;
        //初始化时，必需要输入折扣率，如八折，就是0,8
        public CashRebate(string moneyRebate)
        {
            //界面向类传值
            this.moneyRebate = double.Parse(moneyRebate);
        }
        public override double acceptCash(double money)
        {
            return money * moneyRebate;
        }
    }
}

namespace ExtendDiscountOfSimpleFactoryPattern
{
    //返利收费
    class CashReturn:CashSuper
    {
        private double moneyCondition = 0.0d;
        private double moneyReturn = 0.0d;
        //初始化时必须要输入返利条件和返利值，比如满300返100
        //则moneyCondition为300,moneyReturn为100
        public CashReturn(string moneyCondition, string moneyReturn)
        {
            this.moneyCondition =double.Parse(moneyCondition);
            this.moneyReturn = double.Parse(moneyReturn);
        }

        public override double acceptCash(double money)
        {
            double result = money;
            //若大于返利条件，则需要减去返利值
            if (money >= moneyCondition)
            {
                result = money - Math.Floor(money / moneyCondition) * moneyReturn;
            }
            return result;
        }
    }
}

　　//简单工厂模式类

 namespace ExtendDiscountOfSimpleFactoryPattern
 {
     //收费对象生成工厂
     class CashFactory
     {
         //根据条件返回相应的对象
         public static CashSuper createCashAccept(string type)
         {
             CashSuper cs = null;
             switch (type)
             {
                 case "正常消费":
                     cs = new CashNormal();
                     break;
                 case "满300返100":
                     cs = new CashReturn("", "");
                     break;
                 case "打8折":
                     cs = new CashRebate("0.8");
                     break;
                 case "打7折":
                     cs = new CashRebate("0.7");
                     break;
                 case "打5折":
                     cs = new CashRebate("0.5");
                     break;
             }
             return cs;
         }
     }
 }

　　//在WinForm中调用

　　

 namespace ExtendDiscountOfSimpleFactoryPattern
 {
     public partial class frmMain :Skin_Metro
     {
         public frmMain()
         {
             InitializeComponent();
         }
         //客户端窗体程序
         CashSuper cSuper;//声明一个父类对象

         //声明一个double变量total来计算总计
         double total = 0.0d;
         private void btnConfirm_Click(object sender, EventArgs e)
         {
             //声明一个double变量totalPrices
             double totalPrices = 0d;
            //利用简单工厂模式根据下拉选择框，生成相应的对象
             cSuper = CashFactory.createCashAccept(cbxType.SelectedItem.ToString());
             totalPrices = cSuper.acceptCash(Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text));
             //将每个商品合计计入总计
             total = total + totalPrices;
             //在列表框中显示信息
             lbxList.Items.Add("单价:" + txtPrice.Text + "  数量:" + txtNum.Text + "  合计:" + totalPrices.ToString());
             //在lblTotalShow标签上显示总计数
             lblTotalShow.Text = total.ToString();
         }

         private void btnReset_Click(object sender, EventArgs e)
         {
             total = 0.0;
             txtPrice.Text = "";
             txtNum.Text = "";
             lblTotalShow.Text = "";
             lbxList.Items.Clear();
             cbxType.SelectedIndex = ;
         }

         private void txtNum_KeyPress(object sender, KeyPressEventArgs e)
         {
             //数字0~9所对应的keychar为48~57
             e.Handled = true;
             //输入0-9
             if ((e.KeyChar >=  && e.KeyChar <= ) || e.KeyChar == )
             {
                 e.Handled = false;
             }
         }

         private void txtPrice_KeyPress(object sender, KeyPressEventArgs e)
         {
             //数字0~9所对应的keychar为48~57
             e.Handled = true;
             //输入0-9
             if ((e.KeyChar >=  && e.KeyChar <= ) || e.KeyChar == )
             {
                 e.Handled = false;
             }
         }

         private void frmMain_Load(object sender, EventArgs e)
         {
             //在窗体加载的时候,下拉选择框，就选择索引为0的元素——"正常消费"
             cbxType.SelectedIndex = ;
         }
     }
 }