Java 2D 游戏开发 : Multiple key input

Question

我正在尝试让控件为用 Java 编写的 2D 游戏工作。但是，我在运动中遇到了一个奇怪的错误。每当我尝试在开火时使用向上和向左控件(空格键)，或在开火时使用向下和向右控件时，游戏无法检测到空格键的按下。以下是相关代码摘录:

import java.awt.Image;
import java.awt.event.KeyEvent;
import java.util.ArrayList;
import javax.swing.ImageIcon;

public class Player {
    private String playerPath = "images/craft.png";
    private int x, y, dx, dy;
    private Image image;
    private ArrayList missiles;
    private final int CRAFT_SIZE = 20;

    public Player() {
        ImageIcon ii = new ImageIcon(playerPath);
        image = ii.getImage();
        missiles = new ArrayList();
        x = 20;
        y = 20;
    }
    public void keyPressed(KeyEvent e) {
        int key = e.getKeyCode();
        if (key == KeyEvent.VK_SPACE) {
            fire();
        }
        if (key == KeyEvent.VK_LEFT) {
            dx = -1;
        }
        if (key == KeyEvent.VK_RIGHT) {
            dx = 1;
        }
        if (key == KeyEvent.VK_UP) {
            dy = -1;
        }
        if (key == KeyEvent.VK_DOWN) {
            dy = 1;
        }
    }
    public void keyReleased(KeyEvent e) {
        int key = e.getKeyCode();
        if (key == KeyEvent.VK_LEFT) {
            dx = 0;
        }
        if (key == KeyEvent.VK_RIGHT) {
            dx = 0;
        }
        if (key == KeyEvent.VK_UP) {
            dy = 0;
        }
        if (key == KeyEvent.VK_DOWN) {
            dy = 0;
        }
    }
    public void fire() {
        missiles.add(new Projectile(x + CRAFT_SIZE, y + CRAFT_SIZE/2));
    }
}//end class Player

和

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.util.ArrayList;
import javax.swing.JPanel;
import javax.swing.Timer;

public class Game extends JPanel implements ActionListener {
    private Player player;
    private Timer timer;

    private int winHeight;
    private int winWidth;
    private final int UP = KeyEvent.VK_UP;
    private final int DOWN = KeyEvent.VK_DOWN;
    private final int LEFT = KeyEvent.VK_LEFT;
    private final int RIGHT = KeyEvent.VK_RIGHT;
    private final int SPACE = KeyEvent.VK_SPACE;

    public Game(int w, int h) {
        addKeyListener(new TAdapter());
        setBackground(Color.BLACK);
        addKeyListener(new TAdapter());
        setFocusable(true);
        setDoubleBuffered(true);

        player = new Player();

        winHeight = h;
        winWidth = w;

        timer = new Timer(5, this);
        timer.start();
    }

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

        Graphics2D g2d = (Graphics2D) g;
        g2d.drawImage(player.getImage(), player.getX(), player.getY(), this);

        ArrayList proj = player.getMissiles();

        for (Object p : proj) {
            Projectile b = (Projectile) p;
            g2d.drawImage(b.getImage(), b.getX(), b.getY(), this);
        }

        Toolkit.getDefaultToolkit().sync();
        g.dispose();
    }

    @Override
    public void actionPerformed(ActionEvent e) {

        // Update projectile locations
        ArrayList ms = player.getMissiles();

        for (int i = 0; i < ms.size(); i++) {
            Projectile p = (Projectile) ms.get(i);
            if (p.getX() <= winWidth) {
                p.move();
            } else {
                ms.remove(p);
            }
        }
        player.move();
        repaint();
    }

    private class TAdapter extends KeyAdapter {
        @Override
        public void keyReleased(KeyEvent e) {
            player.keyReleased(e);
        }

        @Override
        public void keyPressed(KeyEvent e) {
            player.keyPressed(e);
        }
    }// end class TAdapter
}// end class Game

Answer 1

Whenever I'm trying to use the up and left controls while firing (space bar), or down and right while firing, the game is unable to detect the pressing of the space bar.

KeyEvents 只为最后一次按下的键生成。如果你想处理同时按下的多个键，那么你需要:

1. 跟踪已按下/释放的键
2. 使用 Swing Timer 来安排动画。

然后每当计时器触发时，您检查当前按下了哪些键并为该键执行操作。