KeyListener 事件显然没有在 Java 小程序中触发

Question

我刚刚开始学习编写小程序和一般的 java GUI，我正在尝试制作一个简单的游戏。目前，我有主类 (Game) 和玩家类 (Player)，我将玩家绘制到屏幕上，但我正在努力让关键事件正常工作，感谢任何帮助！

播放器图像显示非常好，但是当我按下键时位置根本没有改变。

编辑：为播放器发布的错误代码，已更新

Game.java：

public class Game extends Applet {

    Player player;

    @Override
    public void init() {
        player = new Player(this);
        this.setSize(800, 600);
        addKeyListener(player);
    }

    @Override
    public void paint(Graphics g) {        
        player.paint(g);
    }



}

Player.java：

public class Player implements KeyListener {

    Game game;
    Image image;
    int x;
    int y;

    public Player(Game game) {
        this.game = game;
        x = 0;
        y = 0;
        image = game.getImage(game.getCodeBase(), "images/Player.png");
    }

    public void paint(Graphics g) {
        g.drawImage(image, x, y, game);
    }

    @Override
    public void keyTyped(KeyEvent e) {
        return;
    }

    @Override
    public void keyPressed(KeyEvent e) {
        switch (e.getKeyCode()) {
            case KeyEvent.VK_A:
                x -= 1;
                break;
            case KeyEvent.VK_D:
                x += 1;
                break;
            case KeyEvent.VK_S:
                y += 1;
                break;
            case KeyEvent.VK_W:
                y -= 1;
                break;
        }
        game.repaint();
    }

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

Answer 1

面板可能没有焦点，或者无法获得焦点。

---

试试这个代码。我将键更改为左/右/上/下箭头。为简单起见，我将其保留为基于 AWT 的小程序。

// <applet code='Game' width=400 height=100></applet>
import java.applet.*;
import java.awt.*;
import java.awt.event.*;

public class Game extends Applet implements KeyListener {

    Player player;

    @Override
    public void init() {
        player = new Player(getImage(32));
        addKeyListener(this);
        setFocusable(true);
        requestFocusInWindow();
    }

    @Override
    public void paint(Graphics g) {
        player.paint(g);
    }

    public Image getImage(int size) {
        Image img = createImage(size,size);
        Graphics g = img.getGraphics();
        g.setColor(Color.RED);
        g.fillRect(0,0,size,size);

        g.dispose();

        return img;
    }

    @Override
    public void keyTyped(KeyEvent e) {
        return;
    }

    @Override
    public void keyPressed(KeyEvent e) {
        switch (e.getKeyCode()) {
            case KeyEvent.VK_LEFT:
                player.x -= 1;
                break;
            case KeyEvent.VK_RIGHT:
                player.x += 1;
                break;
            case KeyEvent.VK_DOWN:
                player.y += 1;
                break;
            case KeyEvent.VK_UP:
                player.y -= 1;
                break;
        }
        repaint();
    }

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

class Player {

    Image image;
    int x;
    int y;

    public Player(Image image) {
        x = 0;
        y = 0;
        this.image = image;
    }

    public void paint(Graphics g) {
        g.drawImage(image, x, y, null);
    }

}