我的jpanel显得灰色

Question

我试图用按钮制作标题屏幕，并使用 JFrame对象将背景作为图片（BufferedImage）。但是，屏幕显示为灰色，仅在按钮上鼠标鼠标时才更新屏幕的部分。

JFrame类：

//import statements
public class StartGame extends JFrame{
    private JLabel title=new JLabel("Title");
    private JButton start=new JButton("New Game");
    private JButton quit=new JButton("Quit");
    public static final int WIDTH = 1280;
    public static final int HEIGHT = 720;
    public static void main(String [] args){
        StartGame g1=new StartGame();
        g1.play();
    }
    public StartGame(){
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setTitle( "Title" );
        setResizable( false );
        Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
        setSize( WIDTH, HEIGHT );
        setPreferredSize( new Dimension(WIDTH, HEIGHT) );
        setLocation(dim.width/2-getSize().width/2, dim.height/2-getSize().height/2);
        setUndecorated(true);
        setVisible(true);
        StartGamePanel sgp = new StartGamePanel();
        sgp.setSize( StartGame.WIDTH,StartGame.HEIGHT );
        sgp.setLayout( null );
        sgp.setBorder(BorderFactory.createLineBorder(Color.BLACK));
        sgp.setVisible(true);
        start.setBackground(Color.BLACK);
        start.setBorder(BorderFactory.createEmptyBorder());
        start.setBounds( WIDTH/2-105, HEIGHT/9*6, 210, 40 );
        start.setForeground(Color.WHITE);
        quit.setBackground(Color.BLACK);   
        quit.setBorder(BorderFactory.createEmptyBorder());
        quit.setBounds( WIDTH/2-75, HEIGHT/9*8, 150, 40 );
        quit.setForeground(Color.WHITE);
        title.setBounds( WIDTH/2-216, HEIGHT/8*2, 432, 100 );
        title.setForeground(Color.WHITE);
        ButtonListener spy = new ButtonListener();
        start.addActionListener( spy );
        quit.addActionListener( spy );
        sgp.add(title);
        sgp.add(start);
        sgp.add(quit);
        getContentPane().add( sgp );
        pack();
    }
    private void play(){
        EventQueue.invokeLater(new Runnable() {
                public void run() {
                    setVisible(true);
                }
            });
    }
    private class ButtonListener implements ActionListener{
        public void actionPerformed(ActionEvent e) {
            if (e.getSource().equals(quit)) {
                System.exit(0);
            } else if (e.getSource().equals(start)){
                //start
            dispose();
            }
        }
    }
}

和JPanel类：

//import statements
public class StartGamePanel extends JPanel{
    private BufferedImage bg;
    public StartGamePanel(){
        setBackground( Color.WHITE );
        setSize( StartGame.WIDTH, StartGame.HEIGHT );
        setPreferredSize( new Dimension(StartGame.WIDTH, StartGame.HEIGHT) );
        setBorder(BorderFactory.createLineBorder(Color.BLACK));
        setLayout( null );
        try {
            bg = ImageIO.read(new File("pics/SplashScreen.png"));
        } catch (IOException e) {
            System.out.println ( "No splash screen image in StartGamePanel" );
        }
    }
    @Override
    public void paintComponent( Graphics g ) {
        super.paintComponent( g );
        g.drawImage( bg, 0, 0, null );
    }
    private void play(){
        EventQueue.invokeLater(new Runnable() {
                public void run() {
                    setVisible(true);
                }
            });
    }
}

我很确定问题在JPanel类中，因为我能够从程序的另一部分中用另一个JPanel类替换它，并且可以使用。

Answer 1

不在开始时放置 setVisible(true);，或者您之后需要 repaint();。

因为它有时间在底部更新这些添加，这就是为什么您的程序为灰色或Java应用程序的默认颜色。