How do I redraw things when my JFrame is restored (deiconified)?

Question

I have a very basic little JFrame with JToggleButtons and subclassed JPanels that know how to draw what I want them to draw. Selecting a button causes an oval to appear in the corresponding panel. Unselecting the buttons makes the drawings disappear.

Unfortunately, minimizing (iconifying) and then restoring (deiconifying) causes any drawn shapes to disappear. So I need to trigger redrawings manually. The problem is that I can only get the redrawing done (that is, I only see it) if I show a message box first.

Here's the deiconify event for the JFrame:

private void formWindowDeiconified(java.awt.event.WindowEvent evt)
{                                       
    //having this message makes everything work
    JOptionPane.showMessageDialog(null, "Useless message this is.");
    //but if I skip it, I'm SOL
    //what's going on?
    drawAll();
}

This method goes over all of my buttons and asks for the redraws when necessary:

public void drawAll()
{
    for (int i=0; i<channels; i++)
    {
        if (buttons[i].isSelected())
        {
            lightboxes[i].drawMe();            
        }
    }
}

and here is my subclassed JPanel:

class MyJPanel extends JPanel {

    public void drawMe()
    {
        Graphics myGraphics = this.getGraphics();
        myGraphics.fillOval(0, 0, this.getWidth(), this.getHeight());    
    }

    public void unDraw()
    {
        this.invalidate();
        this.repaint();
    }
}

Answer 1

Firstly, for speed I would use double buffering. It's best to paint your graphics off screen and display them to the screen when the drawing has completed. The below should sort you out.

public class MyPanel extends JPanel {
    private BufferedImage buffer;
    private Graphics2D canvas;

    @Override
    public void paintComponent(Graphics g) {
        if(buffer == null) {
            buffer = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_RGB);
            canvas = buffer.createGraphics();
        }
        canvas.fillOval(0, 0, this.getWidth(), this.getHeight());
        g.drawImage(buffer, 0, 0, this);
    }
}