KeyListener的工作，但并不

Question

林新望来的KeyListener，但最近我做了一个小程序，这将是下面，它使用的KeyListener，使A，W，S，d键移动方形。那么我使用Dropbox来获得这台笔记本电脑上的程序，现在它不工作。对我来说这似乎很奇怪，它可以在键盘上使用，但不能在笔记本电脑键盘上使用。任何想法为什么？这里是代码，以及一部分：

public class Game extends JApplet implements KeyListener 
{ 
    public boolean isMoving = false; 
    int test = 0; 
    Rect r = new Rect(); 
      public void keyPressed(KeyEvent e){} 
      public void keyReleased(KeyEvent e){} // ignore 
      public void keyTyped(KeyEvent e) 
      { 
       char keyChar = e.getKeyChar(); 
       if (keyChar == KeyEvent.VK_S) 
        { 
         r.yVelocity -= 1; 
        } 
       if (keyChar == KeyEvent.VK_W) 
        { 
         r.yVelocity+=1; 
        } 
       if (keyChar == KeyEvent.VK_A) 
        { 
         r.xVelocity -=1; 
        } 
       if (keyChar == KeyEvent.VK_D) 
        { 
         r.xVelocity +=1; 
        } 
      } 

Answer 1

KeyListener有焦点问题。也就是说，只有在关注焦点和焦点时才会对关键事件做出响应。

简单的解决方案是将KeyListener注册的组件注册为可聚焦组件，并使用requestFocusInWindow，但这不会让组件接收到关键板的焦点。

一个更好的解决办法是使用Key Bindings API，它允许您配置要提出的关键事件所需的焦点水平...

一键绑定例如更新/测试

import java.awt.BorderLayout; 
import java.awt.Dimension; 
import java.awt.EventQueue; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.event.ActionEvent; 
import java.awt.event.KeyEvent; 
import java.awt.geom.AffineTransform; 
import java.awt.geom.Path2D; 
import java.util.ArrayList; 
import java.util.HashSet; 
import java.util.Set; 
import javax.swing.AbstractAction; 
import javax.swing.ActionMap; 
import javax.swing.InputMap; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.KeyStroke; 
import javax.swing.UIManager; 
import javax.swing.UnsupportedLookAndFeelException; 

public class TestKeyBindings { 

    public static void main(String[] args) { 
     new TestKeyBindings(); 
    } 

    public TestKeyBindings() { 
     EventQueue.invokeLater(new Runnable() { 
      @Override 
      public void run() { 
       try { 
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); 
       } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { 
       } 

       JFrame frame = new JFrame("Testing"); 
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
       frame.setLayout(new BorderLayout()); 
       frame.add(new KeyPane()); 
       frame.pack(); 
       frame.setLocationRelativeTo(null); 
       frame.setVisible(true); 
      } 
     }); 
    } 

    public class KeyPane extends JPanel { 

     private Triangle up; 
     private Triangle down; 
     private Triangle left; 
     private Triangle right; 

     private Set<String> activeKeys; 

     public KeyPane() { 
      activeKeys = new HashSet<>(4); 

      up = new Triangle(20); 
      down = new Triangle(20); 
      left = new Triangle(20); 
      right = new Triangle(20); 

      AffineTransform at = AffineTransform.getRotateInstance(Math.toRadians(-90), 10, 10); 
      left.transform(at); 
      at = AffineTransform.getRotateInstance(Math.toRadians(180), 10, 10); 
      down.transform(at); 
      at = AffineTransform.getRotateInstance(Math.toRadians(-270), 10, 10); 
      right.transform(at); 

      InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW); 
      im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, false), "upPressed"); 
      im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, false), "downPressed"); 
      im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, false), "leftPressed"); 
      im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, false), "rightPressed"); 
      im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, true), "upReleased"); 
      im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, true), "downReleased"); 
      im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, true), "leftReleased"); 
      im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, true), "rightReleased"); 

      ActionMap am = getActionMap(); 
      am.put("upPressed", new DirectionAction("up", true)); 
      am.put("downPressed", new DirectionAction("down", true)); 
      am.put("leftPressed", new DirectionAction("left", true)); 
      am.put("rightPressed", new DirectionAction("right", true)); 
      am.put("upReleased", new DirectionAction("up", false)); 
      am.put("downReleased", new DirectionAction("down", false)); 
      am.put("leftReleased", new DirectionAction("left", false)); 
      am.put("rightReleased", new DirectionAction("right", false)); 
     } 

     public void addKey(String name) { 
      activeKeys.add(name); 
      repaint(); 
     } 

     public void removeKey(String name) { 
      activeKeys.remove(name); 
      repaint(); 
     } 

     @Override 
     public Dimension getPreferredSize() { 
      return new Dimension(200, 200); 
     } 

     @Override 
     protected void paintComponent(Graphics g) { 
      super.paintComponent(g); 
      Graphics2D g2d = (Graphics2D) g.create(); 

      int x = (getWidth() - (up.getBounds().width * 3))/2; 
      int y = (getHeight() - 10)/2; 

      AffineTransform at = AffineTransform.getTranslateInstance(x, y); 
      if (activeKeys.contains("left")) { 
       g2d.fill(left.createTransformedShape(at)); 
      } else { 
       g2d.draw(left.createTransformedShape(at)); 
      } 
      at = AffineTransform.getTranslateInstance(x + 40, y); 
      if (activeKeys.contains("right")) { 
       g2d.fill(right.createTransformedShape(at)); 
      } else { 
       g2d.draw(right.createTransformedShape(at)); 
      } 
      at = AffineTransform.getTranslateInstance(x + 20, y - 20); 
      if (activeKeys.contains("up")) { 
       g2d.fill(up.createTransformedShape(at)); 
      } else { 
       g2d.draw(up.createTransformedShape(at)); 
      } 
      at = AffineTransform.getTranslateInstance(x + 20, y + 20); 
      if (activeKeys.contains("down")) { 
       g2d.fill(down.createTransformedShape(at)); 
      } else { 
       g2d.draw(down.createTransformedShape(at)); 
      } 

      g2d.dispose(); 
     } 

     public class DirectionAction extends AbstractAction { 

      private String name; 
      private boolean pressed; 

      public DirectionAction(String name, boolean pressed) { 
       this.name = name; 
       this.pressed = pressed; 
      } 

      @Override 
      public void actionPerformed(ActionEvent e) { 
       if (pressed) { 
        addKey(name); 
       } else { 
        removeKey(name); 
       } 
      } 

     } 
    } 

    public class Triangle extends Path2D.Double { 

     public Triangle(int size) { 

      moveTo(size/2, 0); 
      lineTo(size, size); 
      lineTo(0, size); 
      closePath(); 

     } 

    } 

}