Question

I am using the netbeans builder “design” on a JFrame class.
I have the traditional JFrame, I added into it (with the builder) a JPanel.

Now in the code, I want to add a background to this panel like this :

public class NewJFrame extends javax.swing.JFrame {

    public NewJFrame() {
        initComponents();
        addBackground();
    }

    private void addBackground()
    {
        Image bgImage;
        try {
            bgImage = ImageIO.read(new File("src/general/Mockup.png"));
            jPanel1.add(new NewJFrame.ImagePanel(bgImage));
            jPanel1.repaint();
        } catch (IOException ex) {
            Logger.getLogger(NewJFrame.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public static void main(String args[]) {

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new NewJFrame().setVisible(true);
            }
        });
    }
}

I don’t see anything, just an empty JFrame/JPanel.

Btw, I am using this for the ImagePanel code

@SuppressWarnings("serial")
class ImagePanel extends JPanel {
    private Image image;

    ImagePanel(Image image) {
        this.image = image;
    };

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(image, 0, 0, getWidth(), getHeight(), this);
    }
}

Answer 1

• your class ImagePanel extends JPanel { must override getPreferredSize(),

• because public void paintComponent(Graphics g) { (painting in Swing, Graphics(2D)) doesn’t returns any size back to the container, simple returns Dimmension(0, 0)

• JPanel has implemented FlowLayout (accepting only PreferredSize that came from its childs) in API, then your custom painting never will be visible on the screen