Java-KeyEvent 方法不起作用

Question

我正在制作一种乒乓球游戏，但我有一个问题。我的代码中有一个方法，用于检查用户输入是否按下了某个键。但当我按下(在我的例子中)UP键时它不会执行。

这是代码，抱歉英语不好，请帮助我:

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

public class GamePanel extends JPanel implements ActionListener,KeyListener{
    Player player = new Player();
    Ball ball = new Ball();

    public GamePanel(){
        Timer time = new Timer(50, this);
        time.start();
    }

    private void update(){
        player.update();
        ball.update();
    }

    public void paintComponent(Graphics g){
        g.setColor(Color.BLACK);
        g.fillRect(0, 0, 800, 600);
        player.paint(g);
        ball.paint(g);
    }
    public void actionPerformed(ActionEvent e){
        update();
        repaint();
    }
    public void keyPressed(KeyEvent e){
        if(e.getKeyCode() == KeyEvent.VK_UP)
        {
            player.setyv(-5);
        }
    }
    public void keyReleased(KeyEvent e){

    }
    public void keyTyped(KeyEvent e){

    }
}

Answer 1

再说一次，

1. 使用按键绑定(bind)而不是 KeyListener，因为这可以帮助您将焦点从图片中移开，而无需使用拼凑。
2. 始终确保在覆盖中调用 super 的paintComponent方法。

例如:

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

public class GamePanel extends JPanel implements ActionListener {
    private static final int PREF_W = 800;
    private static final int PREF_H = 600;
    Player player = new Player();
    Ball ball = new Ball();

    public GamePanel() {
        Timer time = new Timer(50, this);
        time.start();

        // !! set key bindings
        int condition = WHEN_IN_FOCUSED_WINDOW;
        InputMap inputMap = getInputMap(condition);
        ActionMap actionMap = getActionMap();

        KeyStroke up = KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0);
        inputMap.put(up, up.toString());
        actionMap.put(up.toString(), new AbstractAction() {

            @Override
            public void actionPerformed(ActionEvent evt) {
                player.setyv(-5);
            }
        });

        KeyStroke down = KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0);
        inputMap.put(down, down.toString());
        actionMap.put(down.toString(), new AbstractAction() {

            @Override
            public void actionPerformed(ActionEvent evt) {
                player.setyv(5);
            }
        });
    }

    private void update() {
        player.update();
        ball.update();
    }

    // !! public void paintComponent(Graphics g) {
    protected void paintComponent(Graphics g) {
        super.paintComponent(g); // !!
        g.setColor(Color.BLACK);
        g.fillRect(0, 0, PREF_W, PREF_H); // !!
        player.paint(g);
        ball.paint(g);
    }

    // !!
    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        }
        return new Dimension(PREF_W, PREF_H);
    }

    public void actionPerformed(ActionEvent e) {
        update();
        repaint();
    }

    // !!
    private static void createAndShowGui() {
        GamePanel mainPanel = new GamePanel();

        JFrame frame = new JFrame("GamePanel");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

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

interface Playable {
    void update();

    void paint(Graphics g);
}

class Player implements Playable {
    private static final Color PLAYER_COLOR = Color.RED;
    private static final Font FONT = new Font(Font.SANS_SERIF, Font.BOLD, 24);
    private int x = 400;
    private int y = 400;
    private int yv = 0;
    private int xv = 0;

    @Override
    public void update() {
        y += yv;
        x += xv;
    }

    public void setyv(int i) {
        yv += i;
    }

    @Override
    public void paint(Graphics g) {
        g.setFont(FONT);
        g.setColor(PLAYER_COLOR);
        g.drawString("P", x, y);
    }

}

class Ball implements Playable {

    @Override
    public void update() {
        // TODO Auto-generated method stub

    }

    @Override
    public void paint(Graphics g) {
        // TODO Auto-generated method stub

    }

}