JLayeredPane not respecting layers

Question

I have a JLayeredPane. My program works something like this:

JPanel p1 = new JPanel(new BoxLayout(p1, BoxLayout.X_AXIS));
JPanel p2 = new JPanel(new BoxLayout(p2, BoxLayout.Y_AXIS));
JLayeredPane lp = new JLayeredPane();
lp.add(p1, 1);
lp.add(p2, 0);

Both p1 and p2 have components like buttons, etc...

The issue is that when I add both JPanels to the JLayeredPane, NOTHING appears.

I tried changing the layout of the JLayeredPane().

For example, I did:

lp.setLayout(new BoxLayout(lp, BoxLayout.X_AXIS));

Then, the JPanels do show, but they are shown adjacent, not respecting the layers of the JLayeredPane.

Am I forced to use a null layout?

How can I make my JLayeredPane respect the layers and show my two BoxLayout JPanels correctly?

When I give my JLayeredPane a layout, it shows the panels, but it is not respecting the layers at all.

Answer 1

You need a layout manager which understands the Z-Axis. The default layout managers don't understand the Z-Axis of the JLayeredPane.

If you simply want to overlay stuff on top of each other you can use a LayoutManager like this:

JLayeredPane layeredFooPane = new JLayeredPane();
// The magic!
layeredFooPane.setLayout(new LayeredPaneLayout(layeredPane));
// Add components:
layeredFooPane.add(fooComponent, new Integer(JLayeredPane.DEFAULT_LAYER + 10));
layeredFooPane.add(barComponent, JLayeredPane.DEFAULT_LAYER);

LayoutManager Class:

public class LayeredPaneLayout implements LayoutManager {

    private final Container target;
    private static final Dimension preferredSize = new Dimension(500, 500);

    public LayeredPaneLayout(final Container target) {
            this.target = target;
    }

    @Override
    public void addLayoutComponent(final String name, final Component comp) {
    }

    @Override
    public void layoutContainer(final Container container) {
            for (final Component component : container.getComponents()) {
                    component.setBounds(new Rectangle(0, 0, target.getWidth(), target.getHeight()));
            }
    }

    @Override
    public Dimension minimumLayoutSize(final Container parent) {
            return preferredLayoutSize(parent);
    }

    @Override
    public Dimension preferredLayoutSize(final Container parent) {
            return preferredSize;
    }

    @Override
    public void removeLayoutComponent(final Component comp) {
    }
}

Answer 2

The JLayeredPane acts as if it were using null layout. You must specify your JPanel's size and position when adding it to the JLayeredPane. One of the few times I'll recommend this:

JPanel p1 = new JPanel(new BoxLayout(p1, BoxLayout.X_AXIS));
JPanel p2 = new JPanel(new BoxLayout(p2, BoxLayout.Y_AXIS));
JLayeredPane lp = new JLayeredPane();
lp.add(p1, 1);
lp.add(p2, 0);

p1.setSize(lp.getPreferredSize());
p2.setSize(lp.getPreferredSize());

Answer 3

I was having a similar problem. Instead of passing the layer when you add the panes, try to do it separately:

lp.setLayer(p1, 1);
lp.setLayer(p2, 0);
lp.add(p1);
lp.add(p2);

Layers must be defined before adding components. You can also try to use JLayeredPane.DEFAULT_LAYER instead of 0.

In my case, my JLayeredPane had GridBagLayout, I don't know if it works with default layout.