c# - 如何从Button Click事件获取返回值？

Question

我刚刚开始学习C＃。我看到一个古老的问题，有人试图制造可口可乐机器，这似乎是一个很好的练习。

但是我被钱按钮卡住了。我无法弄清楚如何将按钮所代表的金额存储在ColaMachine方法可以访问的变量中。

我有以下代码：

using System;
using System.Windows.Forms;
using System.Drawing;

namespace QuickSharp
{
    public class ColaMachine : Form
    {
        public ColaMachine()
        {
            this.Text = "Cola Machine";
            this.Size = new Size(450 , 500);

            //Money & Money Buttons   

            Label Money;
            Money = new Label();
            Money.Text = "Insert Coins Here:";
            Money.Location = new Point(20, 100);
            this.Controls.Add(Money);

            Button MoneyButton1;
            MoneyButton1 = new Button();
            MoneyButton1.Text = "€0,05";
            MoneyButton1.Location = new Point(28,125);
            MoneyButton1.Click += new System.EventHandler(this.MoneyButton1_Click);
            this.Controls.Add(MoneyButton1);

            Button MoneyButton2;
            MoneyButton2 = new Button();
            MoneyButton2.Text = "€0,10";
            MoneyButton2.Location = new Point(28,165);
            MoneyButton2.Click += new System.EventHandler(this.MoneyButton2_Click);
            this.Controls.Add(MoneyButton2);

            Button MoneyButton3;
            MoneyButton3 = new Button();
            MoneyButton3.Text = "€0,20";
            MoneyButton3.Location = new Point(28,205);
            MoneyButton3.Click += new System.EventHandler(this.MoneyButton3_Click);
            this.Controls.Add(MoneyButton3);

            Button MoneyButton4;
            MoneyButton4 = new Button();
            MoneyButton4.Text = "€0,50";
            MoneyButton4.Location = new Point(28,245);
            MoneyButton4.Click += new System.EventHandler(this.MoneyButton4_Click);
            this.Controls.Add(MoneyButton4);

            Button MoneyButton5;
            MoneyButton5 = new Button();
            MoneyButton5.Text = "€1,00";
            MoneyButton5.Location = new Point(28,285);
            MoneyButton5.Click += new System.EventHandler(this.MoneyButton5_Click);
            this.Controls.Add(MoneyButton5);

            Button MoneyButton6;
            MoneyButton6 = new Button();
            MoneyButton6.Text = "€2,00";
            MoneyButton6.Location = new Point(28,325);
            MoneyButton6.Click += new System.EventHandler(this.MoneyButton6_Click);
            this.Controls.Add(MoneyButton6);

            // Drinks & Drink Buttons

            Label Drinks;
            Drinks = new Label();
            Drinks.Text = "Choose Your Drink:";
            Drinks.Location = new Point(315 , 100);
            Drinks.AutoSize = true;
            this.Controls.Add(Drinks);

            Button DrinkButton1;
            DrinkButton1 = new Button();
            DrinkButton1.Text = "Coca-Cola";
            DrinkButton1.Location = new Point(328,125);
            this.Controls.Add(DrinkButton1);

                        Button DrinkButton2;
            DrinkButton2 = new Button();
            DrinkButton2.Text = "Coca-Cola Light";
            DrinkButton2.Location = new Point(328,165);
            this.Controls.Add(DrinkButton2);

                        Button DrinkButton3;
            DrinkButton3 = new Button();
            DrinkButton3.Text = "Fanta";
            DrinkButton3.Location = new Point(328,205);
            this.Controls.Add(DrinkButton3);

                        Button DrinkButton4;
            DrinkButton4 = new Button();
            DrinkButton4.Text = "Sprite";
            DrinkButton4.Location = new Point(328,245);
            this.Controls.Add(DrinkButton4);

                        Button DrinkButton5;
            DrinkButton5 = new Button();
            DrinkButton5.Text = "Spa Blauw";
            DrinkButton5.Location = new Point(328,285);
            this.Controls.Add(DrinkButton5);

                        Button DrinkButton6;
            DrinkButton6 = new Button();
            DrinkButton6.Text = "Red Bull";
            DrinkButton6.Location = new Point(328,325);
            this.Controls.Add(DrinkButton6);

            //Header & Machine Display

            Label Header;
            Header = new Label();
            Header.Text = "Coca-Cola Machine";
            Header.Font = new Font("Arial" , Header.Font.Size +5);
            Header.ForeColor = Color.DarkRed;
            Header.Location = new Point(132, 20);
            Header.AutoSize = true;
            this.Controls.Add(Header);



            TextBox TextBox1 ;
            TextBox1 = new TextBox();

            if(InsertedCoins == 0.00)
                TextBox1.Text = "Buy Your Ice Cold Drinks Here!";
            else
                TextBox1.Text = "Inserted Coins: €" + InsertedCoins;

            TextBox1.BackColor = Color.Black;
            TextBox1.ForeColor = Color.Red;
            TextBox1.Font = new Font("Arial" , TextBox1.Font.Size +3);
            TextBox1.ReadOnly = true;
            TextBox1.Size = new Size(210,300);
            TextBox1.Location = new Point(112,50);

            // I tried to get the text scrolling here... :)
            TextBox1.SelectionStart = TextBox1.Text.Length;
            TextBox1.ScrollToCaret();
            TextBox1.Refresh();

            this.Controls.Add(TextBox1);
        }


        public double InsertedCoins;

        // Money Button Click Events

        private void MoneyButton1_Click(object sender, EventArgs e)
        {
            InsertedCoins = InsertedCoins + 0.05;
        }

        private void MoneyButton2_Click(object sender, EventArgs e)
        {
            InsertedCoins = InsertedCoins + 0.10;
        }

        private void MoneyButton3_Click(object sender, EventArgs e)
        {
            InsertedCoins = InsertedCoins + 0.20;
        }

        private void MoneyButton4_Click(object sender, EventArgs e)
        {
            InsertedCoins = InsertedCoins + 0.50;
        }

        private void MoneyButton5_Click(object sender, EventArgs e)
        {
            InsertedCoins = InsertedCoins + 1.00;
        }

        private void MoneyButton6_Click(object sender, EventArgs e)
        {
            InsertedCoins = InsertedCoins + 2.00;
        }

        private static void Main()
        {

            ColaMachine Scherm;
            Scherm = new ColaMachine();
            Application.Run(Scherm);
        }
    }
}

另外，如果您对我的常规编程有任何建议（例如，使其他尝试阅读我的代码的人更容易理解），请告诉我！

Answer 1

当我想到可乐机时，我会看到该机中每种饮料的按钮，但看不到用于支付不同金额的按钮。也许您的意思是说可乐要花50美分，所以按可乐按钮我要收50美分。

按钮和事件处理程序

当您按下屏幕上的按钮时，它将生成一个单击事件。您需要编写一种方法来响应该点击。我们用于响应事件的任何方法（通常来说）都称为事件处理程序。您必须告诉程序哪些按钮与事件处理程序一起使用。我们称此为注册事件处理程序

按照约定，如果您的按钮名为“ CokeButton”，则与该特定按钮关联的事件处理程序将命名为“ CokeButton_ClickHandler”。或类似的东西。

一般建议

考虑一下您要建模的事物，并在代码中定义事物以反映现实世界。模型中的事物通常最终会以类，类属性和类字段结尾。这些事情通常会在适当的类中作为方法结束。然后，您考虑这些事物如何相互作用。

在开始编写代码之前，您不需要了解有关炼焦机的所有内容。而且您应该一次写一点点，进行测试，然后在测试的基础上进行构建。不要编写复杂的交互代码，然后进行测试。您最终将转圈追逐您的尾巴。写一点，测试一下，重复一次。现在听我说，以后再相信我。写一点，测试一下，重复一次。永远留意这个建议。

因此，这就是我可能会想到的可乐机。首先是一台可乐机。

public class CokeMachine {}

一台可乐机有一个钱槽，一个返回槽和饮料按钮。我真的不能把钱放在老虎机中，所以我会说我要在文本框中键入内容。然后，我将单击一个按钮，焦炭将被分配。我觉得我已经定义了足够的模型以开始使用。关于可乐机还有很多其他事情，但我现在不担心它们。

但是我需要知道每种饮料要花多少钱。

好吧那么必须有“ CokeCost”，“ 7UpCost”等字段。因此，定义它们！我们将逐步弄清如何以及在何处使用它们。

   public class CokeMachine {
     Button Coke;
     Button 7Up;
     Button RootBeer;
     TextBox MoneySlot;

     double CokeCost = .75;
     double 7UpCost = .65;
}

我说过按钮需要处理程序，因此我们至少可以编写一些代码外壳。我希望它们都能以相同的方式工作，所以我现在将重点介绍一个。请注意，在编写代码时，我意识到必须处理的其他事情。我将添加注释，对尚不存在的方法的调用等。

   public class CokeMachine {
     Button Coke;
     Button 7Up;
     Button RootBeer;
     TextBox MoneySlot;

     double CokeCost = .75;
     double 7UpCost = .65;

     // "wiring up" the coke button click event to it's handler.
     // We do this in C# by declaring an new EventHandler object (a .NET framework supplied class)
     // and we pass in the name of our method as a parameter.
     // This new EventHandler is *added* to the button's click event.
     // An event can have multiple handlers, that's why we do "+="
     // instead of just "=". Otherwise we would have accidentally "unhooked" any
     // previously registered handlers.
     Coke.Click += new EventHandler(Coke_ClickHandler);

     // this is the .NET event handler method signature.
     Public void Coke_ClickHandler (object sender, EventArgs args){
          if (MoneySlot.Value >= CokeCost) {
             DispenseDrink();
             // How do I handle returning change? Maybe DispenseDrink() can do that.
          }else {
             // tell customer to put in more money
          }
     }

     private void DispenseDrink() {
       // An empty method is enough to get it to compile so for now that's fine.
       // I need to test the Coke_EventHandler logic that I've written so far.
     }

  }

现在，我需要测试到目前为止的内容。之后，我需要决定接下来要关注什么。但是要意识到，当您编写依赖于已编写的代码的新代码时，如果该现有代码尚未经过测试-现在您看到错误，那么您自己就会变得更加困难。您可能已经测试了更简单的代码。现在，它变得越来越复杂，并且将更加难以调试和修复。

建议，第二部分

冒着把事情弄乱的风险，我将以下内容提供给我的原始答案：

您会看到每个饮料按钮都执行相同的操作，并且鉴于以上代码，我们将为每个按钮一遍又一遍地编写相同的逻辑。如果需要任何更改，我们必须在任何地方进行更改。

更多一般建议

一种面向对象的编程启发式方法是封装保持不变的方法。您应该始终在寻找可能成为通用代码候选对象的地方。

我想强调，这种常见的按钮行为对我而言并不是立即显而易见的。直到我写完上面的代码后，我才开始想到我所有的饮料按钮处理程序都将看起来相同，并且我意识到在真正的饮料机上，它们实际上的行为方式相同。我的编码间谍意识告诉我们，当代码反映出您真实事物的可识别行为时，这绝对是一件好事（双关语！）。

重构

实际上，这是一个技术术语，意味着对现有代码进行改编以使其更灵活，可重复使用，可读性强。

重构应该一直存在于您的思维过程中。但是请确保您有进行任何更改的正当理由。重塑代码是软件开发的常规组成部分。

让我们通过提取方法进行重构

     Public void Coke_ClickHandler (object sender, EventArgs args){
          PurchaseDrink("Coke", CokeCost);
     }

     // now we have a method that stands out and says THIS is how it works
     // and a single point of change, rather than ump-teen button handlers.
      private PurchaseDrink (string whatKind, double cost) {

         // all I did so far is move the code and change "Cokecost" to "cost"
         // Now I'm beginning to think I may need to pass "whatKind" to
         // DispenseDrink() - but first I need to test the changes I've
         // made at this level.
         // ***** and since I already tested the code when I 1st wrote it,
         // this refactoring will be easier & quicker to test.. GET IT??!! ******

         if (MoneySlot.Value >= cost) {
             DispenseDrink();
             // How do I handle returning change? Maybe DispenseDrink() can do that.
          }else {
             // tell customer to put in more money
          }
     }

     private void DispenseDrink() {
       // An empty method is enough to get it to compile so for now that's fine.
       // I need to test the Coke_EventHandler logic that I've written so far.
     }

枚举

我讨厌像上面使用“可乐”那样使用字符串。错字和大小写（即上/下）可能会导致Visual Studio无法捕获的问题。当我的物品清单很有限时-各种饮料-我真的很喜欢使用枚举。它们显示在智能感知中，我可以在switch语句中使用它们（并研究“类型安全”的概念）。我真正喜欢的是，它们绝对在一处定义了我们程序所知道的所有饮料类型。就像文档！