用于游戏输入捕获的新线程中的键侦听器

Question

我正在用Swing在Java中制作一个老式的贪吃蛇游戏。我已经读到，为了实时捕获输入，我需要在新线程中运行我的游戏循环，以便它wait()方法不会干扰输入捕获。我已经InputCapture类实现了KeyListener并且我已经实现了keyPressed()这样的方法：

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，我制作了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课上，我制作了startNewGame()单击"新游戏"按钮时调用的方法。此方法创建Game对象，并通过调用start()方法启动新线程。

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，它会卡在游戏循环中，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，难道不应该在游戏循环中多次重新绘制吗？

此外，当单击框架的关闭按钮(红色 X 按钮)时，我已经使线程中断，因此执行可以返回到MainMenu并重新出现它，但单击红色关闭按钮不起作用。

Answer 1

由于在startNewGame中调用game.join()，程序冻结。join使调用它的线程不再继续执行，直到调用它的线程死亡。在您的情况下，join违背了使用另一个线程的目的，因此您应该将其删除。

不过，还有其他问题。您可能不应该使用线程。您可能应该使用摆动Timer。Swing 不是线程安全的，我已经可以看到你的代码也不是线程安全的几个地方。(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，只使用计时器会简单得多。

否则，如果您不使用计时器，则需要在游戏线程(写入共享游戏状态)和执行绘画(并且可能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。

另请参阅使用多个 JFrames：好的做法还是坏做法？

Answer 2

你应该使你的Game类扩展Runnable而不是Thread。

然后将游戏置于不同的线程中：

Game theGame = ... // initialization code here
new Thread(theGame).start();