java - 两个 JButtons 使用相同的 actionListener 来启动/停止定时器

Question

我是 Java 的新手，需要一些帮助。我试图让计时器从设定时间倒计时到 0。我的这个功能运行良好，但我想添加功能以允许我在倒计时时停止计时器。

这是我的代码(我正在尝试使用 MVC 实现此目的)

这是控制部分:

import java.awt.event.*;
import javax.swing.*;

public class StartButton extends JButton implements ActionListener
{
    private TimerModel model;
    private Timer timer;
    private boolean isStarted;

    public StartButton(String buttonText, TimerModel model)
    {
        super(buttonText);
        addActionListener(this);
        this.model = model;
        isStarted = false;
    }

    public void actionPerformed(ActionEvent evt)
    {
        if(!isStarted) 
        {
            timer = new Timer(1000, this);
            timer.start();
            isStarted = true;
        }

        model.timerCountdown();
    }

    public void stopTimer()
    {
        timer.stop();
    }
}

我在网上看了一些其他类似的问题，并在构造函数中尝试了这个(注意:我没有使用 implements ActionListener，并删除了上面的 actionPerformed 方法):

if(buttonText.equals("Start"))
    {
        addActionListener(new ActionListener() 
        {
            public void actionPerformed(ActionEvent e)
            {
               if(!isStarted) 
               {
                   timer = new Timer(1000, this);
                   timer.start();
                   isStarted = true;
               }

               model.timerCountdown(); 
            }
        });
    }

    if(buttonText.equals("Stop"))
    {
        addActionListener(new ActionListener() 
        {
            public void actionPerformed(ActionEvent e)
            {
               timer.stop(); 
            }
        });
    }

现在这部分可以正常处理倒计时，但是当我单击停止按钮时它显示异常(See stack trace here)，并且它继续倒计时。

我的知识有限，但我想这与我尝试停止计时器的方式有关。

如果有人能指出正确的方向，或者至少向我解释为什么会这样，我将不胜感激。

Answer 1

同样，如果您不更改 JButton 本身的基本行为，例如它的绘制方式，而只是更改按钮的标题和按下时的行为，则不要扩展 JButton。而是为每个按钮赋予其自己的 Action，一个来自从 AbstractAction 扩展的类的对象。将这些人视为类似于类固醇的 ActionListeners。它们具有与 ActionListeners 相同的功能，还有一些功能，因为它们可以轻松更改按钮的标题(无论是否启用)、它的助记符、图标……

例如:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.Window;
import java.awt.event.*;

import javax.swing.*;

@SuppressWarnings("serial")
public class MyTimerGui {
   private static final String TITLE = "Flashing Label";
   private static final int TIMER_DELAY = 200;
   private static final int GAP = 3;
   private static final float LABEL_POINTS = 32F;
   private JPanel mainPanel = new JPanel();
   private JLabel flashyLabel = new JLabel(TITLE, SwingConstants.CENTER);
   private Timer timer = new Timer(TIMER_DELAY, new TimerListener());

   public MyTimerGui() {
      Font font = flashyLabel.getFont();
      font = font.deriveFont(LABEL_POINTS);
      flashyLabel.setFont(font);
      flashyLabel.setOpaque(true);

      JPanel buttonPanel = new JPanel(new GridLayout(1, 0, GAP, 0));
      buttonPanel.add(new JButton(new StartAction(this, "Start", KeyEvent.VK_S)));
      buttonPanel.add(new JButton(new StopAction(this, "Stop", KeyEvent.VK_T)));
      buttonPanel.add(new JButton(new ExitAction(this, "Exit", KeyEvent.VK_X)));

      mainPanel.setBorder(BorderFactory.createEmptyBorder(GAP, GAP, GAP, GAP));
      mainPanel.setLayout(new BorderLayout());
      mainPanel.add(flashyLabel, BorderLayout.CENTER);
      mainPanel.add(buttonPanel, BorderLayout.PAGE_END);
   }

   public JComponent getMainComponent() {
      return mainPanel;
   }

   public void start() {
      timer.start();
   }

   public void stop() {
      timer.stop();
      flashyLabel.setForeground(null);
      flashyLabel.setBackground(null);
   }

   public void exit() {
      timer.stop();
      Window win = SwingUtilities.getWindowAncestor(mainPanel);
      win.dispose();
   }

   private class TimerListener implements ActionListener {
      private final Color foreground1 = Color.green;
      private final Color background1 = Color.red;

      @Override
      public void actionPerformed(ActionEvent aEvt) {
         Color fg = flashyLabel.getForeground();
         if (foreground1.equals(fg)) {
            flashyLabel.setForeground(null);
            flashyLabel.setBackground(null);
         } else {
            flashyLabel.setForeground(foreground1);
            flashyLabel.setBackground(background1);
         }
      }
   }

   private class StartAction extends AbstractAction {
      private MyTimerGui myTimerGui;

      public StartAction(MyTimerGui myTimerGui, String name, int mnemonic) {
         super(name);
         putValue(MNEMONIC_KEY, mnemonic);
         this.myTimerGui = myTimerGui;
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         myTimerGui.start();
      }
   }

   private class StopAction extends AbstractAction {
      private MyTimerGui myTimerGui;

      public StopAction(MyTimerGui myTimerGui, String name, int mnemonic) {
         super(name);
         putValue(MNEMONIC_KEY, mnemonic);
         this.myTimerGui = myTimerGui;
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         myTimerGui.stop();
      }
   }

   private class ExitAction extends AbstractAction {
      private MyTimerGui myTimerGui;

      public ExitAction(MyTimerGui myTimerGui, String name, int mnemonic) {
         super(name);
         putValue(MNEMONIC_KEY, mnemonic);
         this.myTimerGui = myTimerGui;
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         myTimerGui.exit();
      }
   }

   private static void createAndShowGui() {
      MyTimerGui myTimerGui = new MyTimerGui();

      JFrame frame = new JFrame("MyTimer");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(myTimerGui.getMainComponent());
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}