paint（）方法不会在JPanel上绘制

Question

我尝试了一些用Java绘图的源代码，它们工作正常，但是当我尝试制作自己的源代码时，我无法使用该paint(Grahpics g)方法！我再次查看了自己拥有的代码，并查看了Oracle页面中的一些教程，但是我似乎无法得知为什么它不起作用。有人可以检查一下，告诉我这里有什么问题吗？

主要方法：公共类主要

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

板：

import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;


public class board implements ActionListener
{
    private JFrame f = new JFrame("Speedy");
    private JPanel gamePanel = new JPanel();


    private Image bg = new ImageIcon(this.getClass().getResource("road.png")).getImage();
    private Timer t;


    private car myCar = new car();


    public board()
    {
        t = new Timer(50,this);
        t.start();


        gamePanel.setSize(600,400);
        gamePanel.setDoubleBuffered(true);
        gamePanel.setFocusable(true);
        gamePanel.addKeyListener(new TAdapter());

        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(gamePanel,BorderLayout.CENTER);
        //f.addKeyListener(new TAdapter());
        f.setBounds(200,100,600,400);
        f.setVisible(true);
        f.revalidate();
        f.repaint();

    }




    public void paint(Graphics g) {
        gamePanel.paint(g);

        Graphics2D g2d = (Graphics2D)g;
        g2d.drawImage(bg,0,0,null);
        g2d.drawImage(myCar.getImg(), myCar.xPos, myCar.yPos, null);

        System.out.println("Painted");

        g.dispose();
    }



    public void actionPerformed(ActionEvent e) 
    {
        gamePanel.repaint();
        //System.out.println("Painting..");
    }





    private class TAdapter extends KeyAdapter {

        public void keyReleased(KeyEvent e) {}

        public void keyPressed(KeyEvent e)  
        {
            myCar.keyPressed(e);
            System.out.println("You pressed: "+e);
        }
    }

}

car.java：

    import java.awt.Image;
    import java.awt.event.KeyEvent;
    import java.util.ArrayList;

    import javax.swing.ImageIcon

;



public class car 
{

    private Image image;
    public int xPos,yPos;

    public car()
    {
        image = new ImageIcon(this.getClass().getResource("car.png")).getImage();
        xPos = 300;
        yPos = 200;
        System.out.println(image.getWidth(null));
    }



    public Image getImg() {return image;}


    public void move() {}


    public void keyPressed(KeyEvent e) 
    {

        int key = e.getKeyCode();

        if (key == KeyEvent.VK_LEFT) xPos -= 1;
        if (key == KeyEvent.VK_RIGHT)xPos += 1;
        if (key == KeyEvent.VK_UP)   yPos -= 1;
        if (key == KeyEvent.VK_DOWN) yPos += 1;
    }

}

没有错误，它向我显示了正确的图像宽度，计时器也触发ActionListener，也KeyListener可以正常工作，但是图像无法绘制！该paint(Graphics g)方法只是不想被触发！谷歌搜索它没有帮助..我以为这是一个常见问题，但是没有人遇到我所遇到的问题，所有解决方案都使我失败。请帮助？如果有人可以解释，将不胜感激！

Answer 1

您的课程Board不会扩展JPanel课程。因此paint()，Swing永远不会调用该方法。另外，该语句gamePanel.repaint()将仅执行的默认JPanel
paint()方法gamePanel。相反，您希望执行重写的paint方法，因此可能需要这样做：

public class Board extends JPanel implements ActionListener {
   ....
    public void paint(Graphics g) {
       this.paint(g);

       Graphics2D g2d = (Graphics2D)g;
       g2d.drawImage(bg,0,0,null);
       g2d.drawImage(myCar.getImg(), myCar.xPos, myCar.yPos, null);

       System.out.println("Painted");

       g2d.dispose();
    }
    ....
}

替换为以下功能：

public void actionPerformed(ActionEvent e) {
   this.repaint();
}

替代解决方案： 如果您不希望Board扩展类JPanel，则还可以在初始化它时覆盖paint()方法gamePanel。

gamePanel = new JPanel() {
   @Override
   public void paint(Graphics g) {
       this.paint(g);

       Graphics2D g2d = (Graphics2D)g;
       g2d.drawImage(bg,0,0,null);
       g2d.drawImage(myCar.getImg(), myCar.xPos, myCar.yPos, null);

       g2d.dispose();
   }
};

但是，我建议使用第一个解决方案，而不是使用匿名类的解决方案。