为什么图像不覆盖我的JPanel？

Question

I have been struggling with this for some time. At first, I only used ActionListener, then I added the paintComponent, but I have no idea what to put there. I read some tutorials and used their code as an example, but it still doesn't work. Right now, the end result is the same as it was without PaintComponent.

import java.awt.*;
import javax.swing.*;
import java.awt.event.*; 


public class Scream extends JPanel   {
    private JButton button = new JButton("OK");
    private Color screenColor;
    private JPanel panel = new JPanel(); 
    private JFrame frame;
    private Dimension screenSize;
    private ImageIcon image;
    private JLabel label = new JLabel(image);
    private int x;
    private int y; 
    private boolean mouseClicked;

    public Scream() {

        button.addActionListener(new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e ) {
                if (e.getSource() == button) {
                    mouseClicked = true; 
                    frame.getContentPane().add(label);
                    frame.setSize(image.getIconWidth(), image.getIconHeight()); 
                    panel.repaint();

                }
            }
        });

        frame = new JFrame ("Existential angst");
        screenColor = new Color(150, 100, 0);
        panel.setBackground( screenColor );
        frame.add(button, BorderLayout.PAGE_END);
        frame.add(panel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(1300, 700);
        frame.setVisible(true);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        image.paintComponent(this, g, 1300, 700);
    } 


    public static void main (String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                Scream scream = new Scream();
            }
        });
    }
}

Answer 1

If you are trying to dynamically add an image to a panel then you need to add the label to the panel. There is no need for any custom painting.

The basic code for adding components to a visible GUI is:

panel.add(...);
panel.revalidate();
panel.repaint();

Also, don't attempt to set the size of the frame to the size of the image. A frame contains a titlebar and borders. Instead you can use frame.pack() ;

Answer 2

I noticed a couple of issues:

• image is never initialized to anything so it is null, effectively making the label empty. I assume maybe your example was just incomplete?

• Once I initialized the image to something, your example still did not work. Turns out adding label without specifying any constraint basically does nothing (I assume since adding a component to a border layout without a constraint puts it in the center where panel already is). When I added the label to BorderLayout.NORTH, everything worked (though resizing the frame to the size of the image makes it only partially visible since the frame includes the OK button)