Java Swing: 当按键按下时做某事

Question

我正在使用KeyAdapter获取事件和方法addKeyListener，它正常工作。问题是，当我按下键时，动作只发生一次，而不是在按下键的同时发生动作。只有在按住键3-4秒钟后，动作才会一直发生，这正是我想要的。

我想知道是否有好的方法可以让动作在按下键时就一直发生，而不是在按住3-4秒钟后才开始发生。

我考虑了下一个解决方案，但也许已经有实现的方法了：

public abstract class MyKeyAdapter extends KeyAdapter{
    private boolean isPressed = false;
    private int pressedKey = 0;
    Thread t = new Thread(new Runnable() {
        @Override
        public void run() {
            while(isPressed)
                keyPressedAction(pressedKey);
        }
    });    

    @Override
    public void keyPressed(KeyEvent e) {
            if(!isPressed){
                pressedKey = e.getKeyCode();
                t.start();
            }
    }
    @Override
    public void keyReleased(KeyEvent e) {
         if(isPressed && e.getKeyCode()==pressedKey)}
             isPressed = false;
    }

    public abstract void keyPressedAction(int key);
}

- Alejandro Garcia

Answer 1

我使用键绑定而不是KeyListener，并在按键时启动Swing Timer，在释放 Swing 上停止计时器，这样做已经取得了良好的成功。您可以通过使用KeyStroke.getKeyStroke(int keyCode, int modifiers, boolean onKeyRelease)方法将正确的KeyStroke对象传递到绑定组件的InputMap中来区分键按下和释放。此处可找到KeyStroke API。如果布尔参数为false，则输入将响应按键，如果参数为true，则相反。

以下是一个快速而不太优雅的示例：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;

import javax.swing.*;

@SuppressWarnings("serial")
public class KeyBindingEg extends JPanel {
   private static final String UP_KEY_PRESSED = "up key pressed";
   private static final String UP_KEY_RELEASED = "up key released";
   private static final int UP_TIMER_DELAY = 200;
   private static final Color FLASH_COLOR = Color.red;

   private Timer upTimer;
   private JLabel label = new JLabel();

   public KeyBindingEg() {
      label.setFont(label.getFont().deriveFont(Font.BOLD, 32));
      label.setOpaque(true);
      add(label);

      setPreferredSize(new Dimension(400, 300));

      int condition = WHEN_IN_FOCUSED_WINDOW;
      InputMap inputMap = getInputMap(condition);
      ActionMap actionMap = getActionMap();
      KeyStroke upKeyPressed = KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, false);
      KeyStroke upKeyReleased = KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, true);

      inputMap.put(upKeyPressed, UP_KEY_PRESSED);
      inputMap.put(upKeyReleased, UP_KEY_RELEASED);

      actionMap.put(UP_KEY_PRESSED, new UpAction(false));
      actionMap.put(UP_KEY_RELEASED, new UpAction(true));

   }

   private class UpAction extends AbstractAction {
      private boolean onKeyRelease;

      public UpAction(boolean onKeyRelease) {
         this.onKeyRelease = onKeyRelease;
      }

      @Override
      public void actionPerformed(ActionEvent evt) {
         if (!onKeyRelease) {
            if (upTimer != null && upTimer.isRunning()) {
               return;
            }
            System.out.println("key pressed");
            label.setText(UP_KEY_PRESSED);

            upTimer = new Timer(UP_TIMER_DELAY, new ActionListener() {

               @Override
               public void actionPerformed(ActionEvent e) {
                  Color c = label.getBackground();
                  if (FLASH_COLOR.equals(c)) {
                     label.setBackground(null);
                     label.setForeground(Color.black);
                  } else {
                     label.setBackground(FLASH_COLOR);
                     label.setForeground(Color.white);
                  }
               }
            });
            upTimer.start();
         } else {
            System.out.println("Key released");
            if (upTimer != null && upTimer.isRunning()) {
               upTimer.stop();
               upTimer = null;
            }
            label.setText("");
         }
      }

   }

   private static void createAndShowGui() {
      KeyBindingEg mainPanel = new KeyBindingEg();

      JFrame frame = new JFrame("KeyBindingEg");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

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

- Hovercraft Full Of Eels

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@Pete 我尝试过从下往上以及从上往下运行这段代码，但无法找到在比较中的单词... 这可能与你的技能有关，aaaach。 - mKorbel