java - 为什么我的paintComponent 方法会在我的JButton 上进行绘制？如何使 JPanel 上同时具有 JButton 和图形？

Question

我正在使用两个带有cardLayout 的JPanel，它们都被添加到contentPane 上。每个面板上都有一个 JButton，可切换到另一个面板，但在我的 gridPanel 上，其上有图形，它们似乎覆盖了 JButton，尽管当您单击其位置时它仍然有效，但它是不可见的。如何获得一个既有图形又有 JButton 的 JPanel？非常感谢您的帮助

主类:

public class ProjectileGame extends JPanel
{   
    private static JFrame frame = new JFrame("MyGame");
    private static JPanel panelContent = new JPanel();
    MenuPanel menuPanel = new MenuPanel();
    GridPanel gridPanel = new GridPanel();
    Ball ball = new Ball();

    static CardLayout card = new CardLayout(); 

    public ProjectileGame()
    {   
        frame.setTitle("ProjectileGame");
        frame.add(panelContent);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
        frame.pack();
        frame.setSize(900, 700);

        panelContent.setLayout(card);
        panelContent.add(menuPanel, "1");
        panelContent.add(gridPanel, "2");

        card.show(panelContent, "1");   //First JPanel to be shown is that of the main menu.

        frame.setVisible(true);
    }     

    public static void menuButtonPressed()
    {
        card.show(panelContent, "2");
    }

    public static void gridButtonPressed()
    {
        card.show(panelContent, "1");
    }

    public static void main(String args[])
    {
        new ProjectileGame();
    }
}

gridPanel 类:

public class GridPanel extends JPanel implements ActionListener
{
    private static final Graphics2D g2 = null;
    Ball ball = new Ball();
    JButton backToTheMenu = new JButton("To the Menu");
    Timer timer = new Timer(14, this);

    public GridPanel()
    {
        setOpaque(true);
        setBackground(Color.WHITE);
        setPreferredSize(new Dimension(900, 710));
        add(ball);
        add(backToTheMenu);

        backToTheMenu.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent arg0)
            {       
                ProjectileGame.gridButtonPressed();
            }
        });
    } 

    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);

        Graphics2D g2d1 = (Graphics2D)g;

        ball.paintComponent(g2d1);

        g.setColor(Color.RED);
        g.fillRect(0,  649,  30,  33);

        g.setColor(Color.BLUE);

        for (int i = 0; i < 35; i++)
        {
            g.setColor(Color.GREEN);
            g.drawLine(0, (20+(30*i)),  900,  (20+(30*i)));
            g.drawLine((30+(30*i)), 0, (30+(30*i)), 1000);
        }

        g.setColor(Color.RED);
        g.drawLine(0, 650, 900, 650);
        g.drawLine(30, 0, 30, 1000);

        g.setColor(Color.BLACK);
        g2d1.drawString("X Displacement (metres)", 400, 667);
        AffineTransform at = new AffineTransform();
        at.setToRotation(Math.PI / -1.97);
        g2d1.setTransform(at);
        g2d1.drawString("Y Displacement (metres)", -380, 8);    

    }                 

    public void actionPerformed(ActionEvent e)
    {
        ball.ballPhysics();
        repaint();
        timer.restart();
    }
}

Answer 1

不要向传递给 paintComponent() 方法的 Graphics 对象添加变换和旋转等。这个 Graphics 对象在绘制时会传递给所有其他组件。

相反，您应该创建一个临时Graphics对象来进行绘画:

@Override
protected void paintComponent(Graphics g)
{
    super.paintComponent(g);

    Graphics2D g2d = (Graphics2D)g.create();

    //  do custom painting

    g2d.dispose();
}

现在您需要能够向面板添加多个组件。请注意，您始终可以将另一个面板添加到一个面板中，这样您就可以拥有无​​限的面板嵌套级别。因此，您可以轻松地为 CardLayout 创建两张“卡片”，每张卡片都添加了不同数量的组件。

基础知识是这样的:

JButton button1 = new JButton("Back to Card2") 
JPanel gridPanel = new GridPanel();
JPanel card1 = new JPanel(new BorderLayout());
card1.add(button1, BorderLayout.PAGE_START);
card1.add(gridPanel, BorderLayout.CENTER);

JButton button2 = new JButton("Back to Card1");
JPanel card2 = new JPanel();
card2.add(button2);

JPanel cardPanel = new JPanel();
cardPanel.setLayout( new CardLayout(...) );
cardPanel.add(card1, ...);
cardPanel.add(card2, ...);

frame.add(cardPanel);