Keylistener不为JPanel工作

Question

我正在尝试使用我的JPanel类中的KeyListener按下其中一个箭头键时执行某些操作.这是我的代码:

public class TestPanel extends JPanel implements KeyListener{

    public TestPanel(){
        this.addKeyListener(this);
        this.setFocusable(true);
        this.requestFocusInWindow();
    }

    public void keyPressed(KeyEvent e) {
        if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
            System.out.println("Right");

        }

        if (e.getKeyCode() == KeyEvent.VK_LEFT) {
            System.out.println("Left");
        }

    }

    public void keyTyped(KeyEvent e) {}
    public void keyReleased(KeyEvent e) {}
}

我的main方法将一个新面板实例添加到一个框架并显示它.我需要将keylistener添加到JFrame吗？在我的情况下,这将是困难和低效的,所以如果可能的话,我想让它与这个JPanel一起工作.谁知道我做错了什么？

编辑:键绑定代码不起作用:

public class GamePanel extends JPanel implements ActionListener{

//Constructor
public GamePanel(){

    setupKeyBinding();
    this.setFocusable(true);
    this.requestFocusInWindow();


}

private void setupKeyBinding() {
    int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;
    InputMap inMap = getInputMap(condition);
    ActionMap actMap = getActionMap();

    inMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0), "Left");
    actMap.put("Left", new leftAction());
}

private class leftAction extends AbstractAction {

       public void actionPerformed(ActionEvent e) {
          System.out.println("test");
       }
}

public void actionPerformed(ActionEvent e) {
    //some other game info
}
} 

谁能告诉我为什么这也不起作用？(我的第二个动作听众是我游戏所需的其他东西)

Answer 1

如果您搜索此问题,您将看到它已被询问并已多次解决.

• KeyListeners需要在焦点组件上工作.一种解决方案是在首次使其可聚焦之后为您的组件提供焦点.
• 然而,通过长镜头更好的是使用键绑定.谷歌的教程就此.

请详细了解我对此问题的回答,包括许多血腥细节.

Answer 2

作为参考,我用你的方法创建了一个例子; 虽然它有效,但它也暗示了代码中其他地方的焦点问题.按键绑定避免这种情况,如图所示这里.

附录:这是我的工作密钥绑定.

private static class TestPanel extends JPanel {

    private static final String LEFT = "Left";
    private Action left = new AbstractAction(LEFT) {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println(LEFT);
        }
    };
    private static final String RIGHT = "Right";
    private Action right = new AbstractAction(RIGHT) {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println(RIGHT);
        }
    };

    public TestPanel() {
        this.getInputMap().put(
            KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0), LEFT);
        this.getActionMap().put(LEFT, left);
        this.getInputMap().put(
            KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0), RIGHT);
        this.getActionMap().put(RIGHT, right);
    }
}

原始SSCCE:

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

/**
 * @see https://stackoverflow.com/a/16531380/230513
 */
public class Test {

    private void display() {
        JFrame f = new JFrame("Test");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new TestPanel());
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    private static class TestPanel extends JPanel implements KeyListener {

        public TestPanel() {

            this.addKeyListener(this);
            this.setFocusable(true);
            this.requestFocusInWindow();
        }

        @Override
        public void keyPressed(KeyEvent e) {
            if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
                System.out.println("Right");
            }

            if (e.getKeyCode() == KeyEvent.VK_LEFT) {
                System.out.println("Left");
            }
        }

        @Override
        public void keyTyped(KeyEvent e) {
        }

        @Override
        public void keyReleased(KeyEvent e) {
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Test().display();
            }
        });
    }
}