进入策略模式学习啦。先实现一个笨办法的商场打折收银吧~~

 1     double total = 0.0d;
 2         private void MainFormLoad(object sender, EventArgs e)
 3         {
 4             cbxType.Items.AddRange(new object[] {"正常收费","打八折","打七折","打五折"});
 5             cbxType.SelectedIndex = 0;
 6         }
 7         
 8         void Button1Click(object sender, System.EventArgs e)
 9         {
10             double totalPrices = 0d;
11             switch(cbxType.SelectedIndex)
12             {
13                     case 0:
14                         totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text);
15                         break;
16                     case 1:
17                         totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text) * 0.8;
18                         break;
19                     case 2:
20                         totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text) * 0.7;
21                         break;
22                     case 3:
23                         totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text) * 0.5;
24                         break;
25             }
26             //double totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text);
27             total = total + totalPrices;
28             lbxList.Items.Add("单价： " + txtPrice.Text + "   数量： " + txtNum.Text + "   合计： " + totalPrices.ToString());
29             lblResult.Text = total.ToString();
30         }
31         
32         void Button2Click(object sender, EventArgs e)
33         {
34             txtPrice.Text = Convert.ToString(0.00);
35             txtNum.Text = Convert.ToString(0);
36             lblResult.Text = Convert.ToString(0.00);
37             lbxList.Items.Clear();