How can i make a JPopupMenu transparent?

Question

I'd like to customize the look of JPopupMenu so i made a custom class extending the JPopupMenu class on i overrode the paintComponent method as i would do for any component i need to customize.

public class CustomPopupMenu extends JPopupMenu {

    @Override
    public paintComponent(Graphics g) {
        //custom draw
    }
}

The only problem i have right know is that i'm not able to make the JPopupMenu transparent. I though setOpaque(false) would be enough, i was wrong.

How can i make a JPopupMenu transparent?

Answer 1

The problem with a popup menu is that it may be realized as a top-level container (Window), and a window is opaque, no matter what value you set with setOpaque(), its opaque. But windows can be made translucent, too.

You can hack it by forcing the use of a heavyweight popup and brutally altering its opacity. Try this as a starting base for experiments (Java7):

import java.awt.Window;

import javax.swing.JPopupMenu;
import javax.swing.SwingUtilities;

public class TranslucentPopup extends JPopupMenu {

    {
        // need to disable that to work
        setLightWeightPopupEnabled(false);
    }

    @Override
    public void setVisible(boolean visible) {
        if (visible == isVisible())
            return;
        super.setVisible(visible);
        if (visible) {
            // attempt to set tranparency
            try {
                Window w = SwingUtilities.getWindowAncestor(this);
                w.setOpacity(0.667F);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

}

Note that it will not make submenus translucent!