Java JPanel 不会显示在 JFrame 中

Question

这是我第一次使用 stackoverflow，我遇到了一个我似乎无法深究的问题。我正在尝试独立开发一个小型桌面游戏，它使用一个名为“Frame.java”的类来创建一个包含所有菜单的 JFrame，因此我需要使用一个名为“create()”的方法来返回框架。我还使用了另一个名为“MainPanel.java”的类，它扩展了 JPanel，以创建 MainPanel 的实例以添加到框架的内容 Pane 中。然而，当我运行我的小驱动程序中的所有代码时，似乎没有显示任何内容。任何帮助将不胜感激!

public class MainPanel extends JPanel{

    //the background image of the game
    private BufferedImage img = null; 
    //GUI components of the game
    private JPanel gameWindow, gameWindowHolder, gameInfoHolder, LevelPanel, RevenuePanel,
                    ActionPanel, TimePanel;

    public MainPanel(String path, int width, int height){

        //create BufferedImage based on path
        img = new ImageHelper().createBufferedImage(path);
        //use img to create JPanel gameWindow
        gameWindow = ImageHelper.makeImageComponent(img, width, height);

        gameInfoHolder = new JPanel();
        gameInfoHolder.setPreferredSize(new Dimension(width+10, height+10));
        gameInfoHolder.setBackground(Color.black);
        gameInfoHolder.add(gameWindow);

        //set size of this MainPanel
        setPreferredSize(new Dimension(width+300, height+10));
        //add gameInfoHolder to MainPanel
        add(gameInfoHolder);

    }

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

    }
}

---

public class Driver {


public static void main( String []args){
    JFrame frame = Frame.create();

    JPanel panel = new MainPanel("images/backgrounds/jessicaAlba.jpg", 330, 500);

    frame.getContentPane().add(panel);

    frame.pack();
    frame.setVisible(true);
}

}

---

public class ImageHelper {


//
//Returns an ImageIcon object based on the path
//
public ImageIcon createImageIcon(String path, String description){

    URL imgURL = getClass().getResource(path);
    if (imgURL != null)
        return new ImageIcon(imgURL, description);
    else {
        System.err.println("Couldn't find this file: " + path + ". Check path.");
        return null;
    }
}

//
//Returns an Image object based on the path
//
public Image createImage(String path){

    URL imgURL = getClass().getResource(path);
    Toolkit kit = Toolkit.getDefaultToolkit();

    if (imgURL != null){
        return kit.createImage(imgURL);
    }
    else {
        System.err.println("Couldn't find this file: " + path + ". Check path.");
        return null;
    }

}

//
//Returns a BufferedImage object based on the path
//
public BufferedImage createBufferedImage(String path){
    BufferedImage image;
    URL imgURL = getClass().getResource(path);
    try
    {
        image = ImageIO.read(imgURL);
    }
    catch (IOException e)
    {
        System.err.println("Couldn't find this file: \""+ path +"\". Check path.");
        return null;
    }
    return image;
}

//
//Returns a JPanel object composed of the image found in the path.
//
public static JPanel makeImageComponent(String path, int width, int height){
    BufferedImage image;
    JLabel picLabel;
    ImageIcon icon;

    JPanel panel = new JPanel();
    JPanel panel2 = new JPanel();
    ImageHelper h = new ImageHelper();

    image = h.createBufferedImage(path);
    image = resize(image, width, height);
    icon = new ImageIcon(image);

    panel.setPreferredSize(new Dimension(width, height));
    panel2.setPreferredSize(new Dimension(width+10, height+10));

    panel2.setBackground(Color.black);
    picLabel = new JLabel(icon);
    panel.add(picLabel);
    panel2.add(panel);

    return panel2;
}

//
//Returns a JPanel object composed of the BufferedImage object in the argument
//
public static JPanel makeImageComponent(BufferedImage image, int width, int height){
    JLabel picLabel;
    ImageIcon icon;

    JPanel panel = new JPanel();
    image = resize(image, width, height);
    icon = new ImageIcon(image);
    panel.setPreferredSize(new Dimension(width, height));
    picLabel = new JLabel(icon);
    panel.add(picLabel);

    return panel;
}

//
//Resizes the BufferedImage object to the specified new width and new height.
//
public static BufferedImage resize(BufferedImage img, int newW, int newH) {  
    int w = img.getWidth();  
    int h = img.getHeight();  
    BufferedImage dimg = new BufferedImage(newW, newH, img.getType());  
    Graphics2D g = dimg.createGraphics();  
    g.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);  
    g.drawImage(img, 0, 0, newW, newH, 0, 0, w, h, null);  
    g.dispose();  
    return dimg;  
}
}

Answer 1

当您使用 super.paintComponent 将绘画“堆栈”短路时，不会显示任何内容，因此不会绘制任何子组件。

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

因为这确实没有任何用处，所以可以将其删除并显示添加的面板。