java KeyListener在单击画布后停止工作

Question

我正在做简单的KeyHandler

public class KeyHandler implements KeyListener {
    private final Set<Integer> keyEvents = new LinkedHashSet<>();
    public Set<Integer> pressedKeys() {
        return keyEvents;
    }

    @Override
    public void keyPressed(KeyEvent e) {
        keyEvents.add(e.getKeyCode());
    }

    @Override
    public void keyReleased(KeyEvent e) {
        keyEvents.remove(e.getKeyCode());
    }

    @Override
    public void keyTyped(KeyEvent e) {

    }
}

它被添加到JFrame
frame.addKeyListener(keyListener);

Rest可能是不可逆的，但我将同一个实例传递给KeyBinder

public class KeyBinder {
    private final Map<Integer, GameEvent> bindings = new HashMap<>();
    private final KeyHandler keyHandler;

    public KeyBinder(KeyHandler keyHandler) {
        this.keyHandler = keyHandler;
        bindings.put(KeyEvent.VK_A, MoveEvent.MOVE_LEFT);
        bindings.put(KeyEvent.VK_D, MoveEvent.MOVE_RIGHT);
        bindings.put(KeyEvent.VK_S, MoveEvent.MOVE_DOWN);
        bindings.put(KeyEvent.VK_W, MoveEvent.MOVE_UP);
    }

    public List<GameEvent> mapEvents() {
        final var events = new ArrayList<GameEvent>();
        keyHandler.pressedKeys().forEach(key -> events.add(bindings.get(key)));
        return events;
    }
}

然后，我将这些GameEvents传递到Player实例中，让他移动

@Override
public void update(java.util.List<GameEvent> events) {
    events.forEach(this::handleEvent);
}

private void handleEvent(GameEvent event) {
    if (event instanceof MoveEvent) {
        updatePosition((MoveEvent) event);
    }
}

private void updatePosition(MoveEvent event) {
    switch (event) {
        case MOVE_UP -> position = new Position(position.getX(), position.getY() - speed);
        case MOVE_DOWN -> position = new Position(position.getX(), position.getY() + speed);
        case MOVE_RIGHT -> position = new Position(position.getX() + speed, position.getY());
        case MOVE_LEFT -> position = new Position(position.getX() - speed, position.getY());
    }
}

如果我只运行应用程序的一个实例，它就可以正常工作。但由于这是一个在线游戏，我想同时运行两个实例进行测试。不幸的是，当我启动第二个实例时，我的KeyHandler在任何一个实例中都不再有效，它只是不记录任何KeyEvents。我知道我的应用程序还在运行，因为我的服务器应用程序一直在从两个客户端接收数据

编辑：

我刚刚意识到还有其他问题KeyHandler单击画布后停止工作。。。我甚至不需要第二次申请。这是我用来画东西的JFrame和Canvas的代码

 public class Display {
        private JFrame frame;
        private Canvas canvas;
    
        public Display(KeyListener keyListener) {
            initFrame(keyListener);
            initCanvas();
            frame.add(canvas);
            frame.pack();
        }
    
        private void initFrame(KeyListener keyListener) {
            frame = new JFrame(GameConfig.TITLE);
            frame.setSize(GameConfig.SCREEN_WIDTH, GameConfig.SCREEN_HEIGHT);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setResizable(false);
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
            frame.addKeyListener(keyListener);
        }
    
        private void initCanvas() {
            canvas = new Canvas();
            canvas.setPreferredSize(new Dimension(GameConfig.SCREEN_WIDTH, GameConfig.SCREEN_HEIGHT));
            canvas.setMaximumSize(new Dimension(GameConfig.SCREEN_WIDTH, GameConfig.SCREEN_HEIGHT));
            canvas.setMinimumSize(new Dimension(GameConfig.SCREEN_WIDTH, GameConfig.SCREEN_HEIGHT));
        }
    
        public Canvas getCanvas() {
            return canvas;
        }
    }

Answer 1

keylistener不监听任何keyevents的原因是，keylistener仅在组件具有焦点时工作。似乎当你点击画布时，画布现在是焦点的所有者，因此画面不再聚焦

一般来说，我建议使用密钥绑定。即使组件没有聚焦，键绑定也可以监听keyevents。但如果你想继续使用KeyListener，这里有两个解决方案：

Add a FocusListener to the frame.

    frame.addFocusListener(new FocusListener() {
            public void focusGained(FocusEvent e) {}
            public void focusLost(FocusEvent e) {frame.requestFocus();}
    });

Disable the focusability of canvas.

    canvas.setFocusable(false);

我们不推荐这些解决方案，但它应该适合您的情况