java - 当我将 jframe 作为参数传递给另一个方法时，出现空白帧

Question

我正在创建一个小游戏，有一个带有按钮的菜单方法可以启动实际的游戏。我只想要一帧来完成所有这些，但是当我将 jframe 作为参数传递给游戏方法时，游戏就变成了空白帧。

这是我的代码。我使用调试器并发现 Paint 方法从未被调用。

    public class GameMenu
    {
        public void start()
        {
            JFrame frame = new JFrame();
            frame.setSize(480,600);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setResizable(false);
            frame.setVisible(true);


      Background background = new Background(frame);
    }
}

    public class Background extends JPanel implements KeyListener , ActionListener
{
    private JFrame frame;
    private Player player1;
    private ObstacleControl obsControl;
    private SpeedBuffControl spdBuffControl;
    private ExtraLifeControl lifeControl;
    private Timer timer;
    private int lifeCount;
    private int xLeft;
    private int xRight;
    private int yDown;
    private int yUp;

    public Background(JFrame frame)
    {
        frame.add(this);
        startGame();
    }

    public void startGame()
    {
        timer = new Timer(20000,this);

        obsControl = new ObstacleControl(this);
        spdBuffControl = new SpeedBuffControl(this);
        lifeControl = new ExtraLifeControl(this);

        timer.start();
        player1 = new Player(this); 
        lifeCount = 3;
        xLeft = -4;
        xRight = 4;
        yDown = 4;
        yUp = -4;
    }

    public void resetPlayer()
    {
        if(lifeCount>1)
        {
            player1 = new Player(this);
            obsControl.resetObstacle();
            lifeCount--;
        }
        else
            System.out.println("you are dead");
    }

    public void actionPerformed(ActionEvent event)
    {
        obsControl.increaseDifficulty();
        spdBuffControl.addBuff();
        lifeControl.addExtraLife();
    }

    public void paint(Graphics g)
    {
        g.setColor(new Color(149,146,240));
        g.fillRect(0,0,480,600);
        player1.draw(g);
        obsControl.draw(g);
        spdBuffControl.draw(g);
        lifeControl.draw(g);
        g.dispose();
        repaint();
    }

Answer 1

Swing 在更新布局时很懒

而不是

frame.setVisible(true);
Background background = new Background(frame);

你应该做...

Background background = new Background(frame);       
frame.setVisible(true);

但这引出了一个问题:为什么你会这么麻烦，相反，你真的应该这样做......

JFrame frame = new JFrame();
frame.setResizable(false);
frame.setSize(480,600);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new Background());
frame.setVisible(true);

并且不将JFrame传递给Background，它不需要它

这在很多层面上都是错误的......

public void paint(Graphics g)
{
    g.setColor(new Color(149,146,240));
    g.fillRect(0,0,480,600);
    player1.draw(g);
    obsControl.draw(g);
    spdBuffControl.draw(g);
    lifeControl.draw(g);
    g.dispose();
    repaint();
}

• 根据喜好，您应该使用 paintComponent 而不是 paint
• 在进行任何自定义绘画之前，您应该调用方法 super 方法
• 您不应在并非您创建的 Graphics 上下文上调用 dispose
• 您不应在 Paint 方法中调用 repaint(或调用任何可能调用 repaint 的方法)

看看Painting in AWT and Swing和 Performing Custom Painting了解更多详情