在Java按键上启动计时器

Question

I want to, when i click the "d" button, start a timer. This is to animate a player walking. The timer doesn't start when i press the key, how do i do that?

The code I have is this:

public class Game extends JPanel implements KeyListener {
//Player variables
private BufferedImage playerStanding;
private BufferedImage playerWalking;
private BufferedImage playerFrame;
private boolean walking = false;
private final int PLAYER_HEIGHT = 100;
private final int PLAYER_WIDTH = 100;
private final int INITIAL_X = 0;
private final int INITIAL_Y = 500;
private int x = INITIAL_X;
private int y = INITIAL_Y;
//The timer I want to start on keypress-> "d"
private Timer playerAnimationTimer;



public Game() {
    setPreferredSize(new Dimension(800, 800));
    setBackground(Color.CYAN);
    //Player
    try {
        playerStanding = ImageIO.read(getClass().getResource("player1.gif"));
        playerWalking = ImageIO.read(getClass().getResource("player2.gif"));
        playerFrame = playerStanding;


    }
    catch (IOException ex) {
        ex.printStackTrace();
    }

    playerAnimationTimer = new Timer(500, new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            walking = !walking;
            playerFrame = walking ? playerWalking : playerStanding;
            x += 10;
            if (x > getWidth() - PLAYER_WIDTH) {
                x = INITIAL_X;
            }
            repaint();
        }
    });
    playerAnimationTimer.setRepeats(true);
}

public Dimension setPreferredSize() {
    return new Dimension(800, 800);
}



@Override
public void paintComponent(Graphics graphics) {
    super.paintComponent(graphics);

    Graphics2D graphics2D = (Graphics2D) graphics;
    if (playerFrame != null) {
        graphics2D.drawImage(playerFrame, x, y, PLAYER_WIDTH, PLAYER_HEIGHT, this);
    }


    graphics2D.dispose();
}

@Override
public void keyTyped(KeyEvent e) {
    //This doesn't work
    playerAnimationTimer.start();
}

@Override
public void keyPressed(KeyEvent e) {

}

@Override
public void keyReleased(KeyEvent e) {

}
}
//The class to hold the gamepanel
public class StartGame extends JFrame implements ActionListener {
private static JButton startGame = new JButton();

StartGame() {
    setDefaultCloseOperation(WindowConstants.HIDE_ON_CLOSE);
    setSize(200, 100);
    setVisible(true);
    setBackground(Color.BLUE);
    setLocationRelativeTo(null);

    startGame.setText("Play!");
    startGame.setSize(100, 25);
    startGame.addActionListener(this);
    add(startGame);
}

@Override
public void actionPerformed(ActionEvent e) {
    if (e.getSource() == startGame) {
        this.setVisible(false);
        new GameWindow();
    }
}
public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            new StartGame();
        }
    });
}
}

How could I make the timer start when I click the "d" button?

Answer 1

Your KeyListener doesn't work because you never add the KeyListener to anything much less to a component that has focus, which is needed for a KeyListener to work.

I suggest that you instead use Key Bindings as a cleaner safer way to capture the desired key press.

As an aside, never dispose of a Graphics object that is given to you from the JVM.

For a better answer, please edit your code to make it comply with the mcve standard. You should use no images files, and it should compile and run for us unaltered.

Answer 2

You could set the private Timer like you did and start it like this...

public void startTimer(){
   timer.start();
   timer.setRepeats(true);
}