Question

I have the following Java Swing problem: a parent panel doesn’t get painted (i.e. paintComponent() not even called) when it is covered by another panel which has a transparent background.

I guess this behavior is normal if the child panel isn’t transparent but here it is an issue since the parent panel provides a picture as background.

Probably not relevant but you never know: child panel is a ChartPanel from JFreeChart’s library (extends JPanel) and parent panel is also a JPanel extension, hereby the paintComponent code:

@Override

public void paintComponent(Graphics g) {
    try {
        long start = System.currentTimeMillis();

        //Sets waiting cursor
        GuiHelper.setCursorOnEntireWindow(Cursor.WAIT_CURSOR);

        //Paints parent
        super.paintComponent(g);

        //Paints background and other elements
        g.drawImage(generateBackground(getWidth(), getHeight()), 0, 0, getWidth(), getHeight(), this);

        long end = System.currentTimeMillis();
        System.out.println("Chart paint took: "+(end-start)+"ms");
    }
    finally { 
        //Removes waiting cursor
        GuiHelper.setCursorOnEntireWindow(Cursor.getDefaultCursor().getType()); 
    }       

}

Any help/hint would be greatly appreciated as I’ve been looking into for hours now.

Thanks!

Answer 1

a parent panel doesn’t get painted (i.e. paintComponent() not even called) when it is covered by another panel which has a transparent background

Not sure how you are setting the transparent background of ChartPanel. I think you just need to use:

childPanel.setOpaque(false);

If this doesen’t work then check out Background With Transparency for more information on how painting is done between child/parent components.