java - 形状在绘图面板java上不移动

Question

我正在尝试用 bat (桨)和球制作一个简单的java游戏。到目前为止，我已将这两个对象绘制到面板上，但是我无法让它们移动。我为球棒添加了关键事件，为球添加了 move() 方法。以下是我的所有类(class)。

游戏类:

public class Game extends JFrame {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new Game();
            }});
    }

    MyDrawingPanel myDrawingPanel = new MyDrawingPanel(this);
    MyUIPanel myUIPanel = new MyUIPanel(this);


    public Game()
    {
        setSize(1160,660); // you may change frame and panel sizes
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        Container cp = getContentPane();    
        cp.setLayout(new FlowLayout());
        cp.add(myDrawingPanel);
        cp.add(myUIPanel);

        setVisible(true);
    }
}

MyDrawingPanel 类:

class MyDrawingPanel extends JPanel {

    Game game;

    Ball ball = new Ball(this);
    Bat bat = new Bat(this);

    public MyDrawingPanel(Game game)
    {
        this.game=game;
        setPreferredSize(new Dimension(800,600));
        setBackground(Color.RED);
        requestFocus();
    }

    public void paint(Graphics g)
    {
        super.paint(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
        ball.paint(g2d);

        Graphics2D gBat = (Graphics2D) g;
        bat.paint(gBat);
    }
}

球类:

public class Ball {

    int x = 0;
    int y = 0;
    int xa = 1;
    int ya = 1;
    private MyDrawingPanel myDrawingPanel;

    public Ball(MyDrawingPanel myDrawingPanel) {
        this.myDrawingPanel = myDrawingPanel;
    }

    public void move() {
        if (x + xa < 0)
            xa = 1;
        if (x + xa > myDrawingPanel.getWidth() - 30)
            xa = -1;
        if (y + ya < 0)
            ya = 1;
        if (y + ya > myDrawingPanel.getHeight() - 30)
            ya = -1;

        x = x + xa;
        y = y + ya;
    }

    public void paint(Graphics2D  g) {
        g.fillOval(x, y, 30, 30);
    }
}

bat 类:

public class Bat{

    int x = 0;
    int xa = 0;
    private MyDrawingPanel myDrawingPanel;

    public Bat(MyDrawingPanel myDrawingPanel)
    {
        this.myDrawingPanel = myDrawingPanel;
    }

    public void move(){
        if(x + xa > 0 && x + xa <myDrawingPanel.getWidth()-60 )
            x = x + xa;
    }

    public void paint(Graphics2D g)
    {
        g.setColor(Color.BLUE);
        g.fillRoundRect(x, 500, 100, 20, 10, 10);
    }

    public void keyPressed(KeyEvent e)
    {
        if(e.getKeyCode() == KeyEvent.VK_LEFT)
            xa = -1;
        if(e.getKeyCode() == KeyEvent.VK_RIGHT)
            xa = 1;
    }

    public void keyReleased(KeyEvent e)
    {
        xa = 0;
    }
}

Answer 1

如果没有 KeyListener 实现，keyPressed 和 keyReleased 等方法不会执行任何操作。所以目前来说，你的方法是没有用的。您应该让 DrawingPanel 类实现 KeyListener，如下所示

public class DrawingPanel extends JPanel implements KeyListener {
    ...
}

方法 keyPressed 和 keyReleased 应该位于该类中。您还需要使用 setter 方法来更新 Bat 类中的变量，例如 x 和 xa ，是决定 bat 运动的变量。

因此，在应该位于 DrawingPanel 类中的 keyPressed 中，它可能看起来像这样

public void keyPressed(KeyEvent e) {
    if (e.getKeyCode() == KeyEvent.VK_LEFT) {
        bat.setXa(bat.getXa() - 1);
        repaint();
    }
    if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
        bat.setXa(1);
        repaint();
    }
}

注意我如何调用repaint()。这就是您移动某些内容后需要执行的操作。

这应该让您朝着正确的方向开始

<小时/>

编辑

忘记上面答案的大部分内容。

尽管我建议使用键绑定(bind)，而不是使用KeyListener。使用KeyListener时您可能会遇到焦点问题。我为 DrawingPanel 实现了键绑定(bind)，并且工作正常。它会给你一些可以使用的想法。

class MyDrawingPanel extends JPanel {

    Game game;

    Ball ball = new Ball(this);
    Bat bat = new Bat(this);

    public MyDrawingPanel(Game game) {
        this.game = game;
        setPreferredSize(new Dimension(800, 600));
        setBackground(Color.RED);
        requestFocus();

        Action rightAction = new AbstractAction() {
            public void actionPerformed(ActionEvent e) {
                bat.x += 10;
                repaint();
            }
        };
        Action leftAction = new AbstractAction() {
            public void actionPerformed(ActionEvent e) {
                bat.x -= 10;
                repaint();
            }
        };

        InputMap inputMap = getInputMap(JPanel.WHEN_IN_FOCUSED_WINDOW);
        ActionMap actionMap = getActionMap();

        inputMap.put(KeyStroke.getKeyStroke("RIGHT"), "rightAction");
        actionMap.put("rightAction", rightAction);
        inputMap.put(KeyStroke.getKeyStroke("LEFT"), "leftAction");
        actionMap.put("leftAction", leftAction);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        ball.paint(g2d);

        Graphics2D gBat = (Graphics2D) g;
        bat.paint(gBat);
    }
}

<小时/>

参见How to use key bindings