java - 新线程中的 KeyListener 用于捕获游戏输入

Question

我正在用 Java 用 Swing 制作一个老式的贪吃蛇游戏。我读过，为了实时捕获输入，我需要在新线程中运行游戏循环，以便它的 wait() 方法不会干扰输入捕获。我已经创建了 InputCapture 类来实现 KeyListener 并实现了 keyPressed() 方法，如下所示:

public class InputCapture implements KeyListener {

    private Direction capturedDirection;

    //Methods
    @Override
    public void keyPressed(KeyEvent e) {
        boolean inputConsoleDebug = true;
        if (e.getKeyCode() == KeyEvent.VK_LEFT) {
            capturedDirection = Direction.left;
            if (inputConsoleDebug) System.out.println("LEFT");
        } else if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
            capturedDirection = Direction.right;
            if (inputConsoleDebug) System.out.println("RIGHT");
        } else if (e.getKeyCode() == KeyEvent.VK_UP) {
            capturedDirection = Direction.up;
            if (inputConsoleDebug) System.out.println("UP");
        } else if (e.getKeyCode() == KeyEvent.VK_DOWN) {
            capturedDirection = Direction.down;
            if (inputConsoleDebug) System.out.println("DOWN");
        }
    }

    @Override
    public void keyReleased(KeyEvent e) {
    }

    @Override
    public void keyTyped(KeyEvent e) {
    }

    public Direction getCapturedDirection() {
        return capturedDirection;
    }
}

然后我创建了 Game 类扩展 Thread 并将游戏循环代码放入 run() 方法中:

public class Game extends Thread {

    private Board board;
    private Snake snake;
    private JFrame frame;
    private long waitTime;
    private int difficultyStep;
    private Direction inputDirection;
    private InputCapture inputManager;

    //Constructors
    Game(Dimension boardSize) {
        //Set difficulty
        int applesToWin = boardSize.width * boardSize.height - 1;
        final int easiestWaitTime = 1000;
        final int hardestWaitTime = 100;
        difficultyStep = (easiestWaitTime - hardestWaitTime) / applesToWin;
        waitTime = easiestWaitTime;
        //Set starting point
        final int startingPointX = boardSize.width / 2;
        final int startingPointy = boardSize.height / 2;
        //Set board and snake
        board = new Board(boardSize);
        snake = new Snake(board, startingPointX, startingPointy);
        //Set window Frame
        frame = new JFrame(SnakeApplication.getApplicationName());
        frame.setContentPane(board);
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.pack();
        frame.setResizable(false);
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                super.windowClosing(e);
                interrupt();
            }
        });
        //Set input manager
        inputManager = new InputCapture();
        frame.addKeyListener(inputManager);
        inputDirection = null;
    }

    //Methods
    public void run() {
        board.spawnApple();
        while (!isWon()) {
            try {
                sleep(waitTime);
            } catch (InterruptedException e) {
                return;
            }
            try {
                inputDirection = inputManager.getCapturedDirection();
                snake.move(inputDirection);
            } catch (LosingMove e) {
                showGameOverDialog();
                return;
            }
            board.repaint();
        }
        showWinDialog();
    }

    JFrame getFrame() {
        return frame;
    }

    private boolean isWon() {
        for (int row = 0; row < board.getFields().length; row++) {
            for (int col = 0; col < board.getFields()[0].length; col++) {
                if (!(board.getFields()[row][col].getContent() instanceof Snake.SnakeNode)) return false;
            }
        }
        return true;
    }

    private void showGameOverDialog() {
        JFrame gameOverFrame = new JFrame();
        JOptionPane.showMessageDialog(gameOverFrame, "Game Over!");
    }

    private void showWinDialog() {
        JFrame gameOverFrame = new JFrame();
        JOptionPane.showMessageDialog(gameOverFrame, "You Win!");
    }
}

在我的 MainMenu 类中，我创建了 startNewGame() 方法，单击“新游戏”按钮时会调用该方法。此方法创建 Game 对象并通过调用 start() 方法启动一个新线程。

public class MainMenu {

    //Form components references
    private JButton exitButton;
    private JFrame frame;
    private JPanel mainPanel;
    private JButton newGameButton;
    private JLabel titleLabel;

    //Constructors
    MainMenu() {
        //Set window Frame
        frame = new JFrame(SnakeApplication.getApplicationName());
        frame.setContentPane(mainPanel);
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.setResizable(false);
        frame.pack();
        newGameButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                startNewGame();
            }
        });
        exitButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                exitGame();
            }
        });
    }

    JFrame getFrame() {
        return frame;
    }

    private Dimension showBoardSizeDialog() {
        Frame boardSizeFrame = new Frame();
        int width = Integer.parseInt(JOptionPane.showInputDialog(boardSizeFrame, "Set board's width:"));
        int height = Integer.parseInt(JOptionPane.showInputDialog(boardSizeFrame, "Set board's height:"));
        return new Dimension(width, height);
    }

    private void startNewGame() {
        Dimension boardSize = showBoardSizeDialog();
        frame.setVisible(false);
        Game game = new Game(boardSize);
        game.getFrame().setVisible(true);
        //Starting game loop in a new thread
        game.start();
        try {
            game.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        frame.setVisible(true);
    }
}

但是在测试应用程序时，它会陷入游戏循环中并且根本不捕获输入。为什么？我试图调试它，但每次启动新线程时，它都会卡在游戏循环中。仅当主线程结束其执行时，才会绘制 Board 本身。为什么？如果执行卡在那里，不应该在游戏循环期间重新绘制很多次吗？

此外，当单击框架的关闭按钮(红色 X 按钮)时，我会中断线程，因此执行可以返回到 MainMenu 并重新出现，但单击红色关闭按钮没有任何效果。

Answer 1

程序由于在 startNewGame 中调用 game.join() 而卡住。 join 阻止调用它的线程继续执行，直到调用它的线程终止。在您的情况下，join 违背了使用另一个线程的目的，因此您应该删除它。

不过，还有其他问题。您可能不应该使用线程。 You should probably use a Swing Timer 。 Swing isn't thread-safe ，而且我已经可以看到您的代码在一些地方也不是线程安全的。 (例如，您需要将 capturedDirection 声明为 volatile 。)使用 Swing 编写正确的多线程代码有点复杂，仅使用计时器会简单得多.

否则，如果您不使用计时器，则需要使用例如游戏线程(写入共享游戏状态)和进行绘画的 Swing 线程(大概从共享游戏状态读取)之间的同步。如果不这样做，您可能会遇到难以诊断的问题。

另请参阅The Use of Multiple JFrames: Good or Bad Practice?