java为什么我的KeyListener不读取键？

Question

我正在用JPanel和Graphics来做游戏。我已经实现了一个KeyListener，并将它添加到了我的JPanel。然而，我无法让它读取钥匙码。我添加了一个print语句，我假设它会在按下某个键时打印，但我按下的键都不会返回代码。这是我的JPanel构造函数：

public Game()
{
    super();
    JPanel mazepanel = new JPanel();
    this.add(mazepanel);
    this.setVisible(true);
    this.addMouseListener(this);
    this.addKeyListener(this);
}

这是我的KeyListener

public void keyTyped(KeyEvent kb)
{
    System.out.println("Key pressed: " + kb.getKeyCode());
    if (kb.getKeyCode() == KeyEvent.VK_UP)
    {
        forward = true;
    }
    else if (kb.getKeyCode() == KeyEvent.VK_LEFT)
    {
        left = true;
    }
    else if (kb.getKeyCode() == KeyEvent.VK_RIGHT)
    {
        right = true;
    }
    else if (kb.getKeyCode() == KeyEvent.VK_DOWN)
    {
        back = true;
    }
    else
    {

    }

    this.repaint();
}

Answer 1

默认情况下，您的JPanel不可聚焦。加

setFocusable(true);

这样做

Answer 2

下面是一个使用KeyListener的好例子：

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;
import javax.swing.JPanel;

@SuppressWarnings("serial")
public class KeyboardExample extends JPanel {

    public KeyboardExample() {
        KeyListener listener = new MyKeyListener();
        addKeyListener(listener);
        setFocusable(true);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Mini Tennis");
        KeyboardExample keyboardExample = new KeyboardExample();
        frame.add(keyboardExample);
        frame.setSize(200, 200);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public class MyKeyListener implements KeyListener {
        @Override
        public void keyTyped(KeyEvent e) {
        }

        @Override
        public void keyPressed(KeyEvent e) {
            System.out.println("keyPressed="+KeyEvent.getKeyText(e.getKeyCode()));
        }

        @Override
        public void keyReleased(KeyEvent e) {
            System.out.println("keyReleased="+KeyEvent.getKeyText(e.getKeyCode()));
        }
    }
}

从http://www.edu4java.com/en/game/game4.html