Панель диспетчера слоёв WorldWind пуста

Question

Я занимаюсь разработкой приложения WorldWind и хочу повторно использовать пример класса LayerAndElevationManagerPanel в своем собственном приложении. Я пытаюсь поместить его в диалоговое окно, которое пользователь может вызвать по требованию, однако, когда диалоговое окно отображается, панель прокрутки для панели пуста. Можно ли использовать этот пример повторно?

Вот пример кода от WorldWind

/*
 * Copyright (C) 2013 United States Government as represented by the Administrator of the
 * National Aeronautics and Space Administration.
 * All Rights Reserved.
 */

package gov.nasa.worldwindx.examples.layermanager;

import gov.nasa.worldwind.WorldWindow;

import javax.swing.*;
import java.awt.*;

/**
 * Combines the layer manager and elevation model manager in a single frame.
 *
 * @author tag
 * @version $Id$
 */
public class LayerAndElevationManagerPanel extends JPanel
{
    protected LayerManagerPanel layerManagerPanel;
    protected ElevationModelManagerPanel elevationModelManagerPanel;

    public LayerAndElevationManagerPanel(WorldWindow wwd)
    {
        super(new BorderLayout(10, 10));

        this.add(this.layerManagerPanel = new LayerManagerPanel(wwd), BorderLayout.CENTER);

        this.add(this.elevationModelManagerPanel = new ElevationModelManagerPanel(wwd), BorderLayout.SOUTH);
    }

    public void updateLayers(WorldWindow wwd)
    {
        this.layerManagerPanel.update(wwd);
    }

    public void updateElevations(WorldWindow wwd)
    {
        this.elevationModelManagerPanel.update(wwd);
    }

    public void update(WorldWindow wwd)
    {
        this.updateLayers(wwd);
        this.updateElevations(wwd);
    }
}

Вот мой код

import java.awt.BorderLayout;
import java.awt.FlowLayout;

import javax.swing.GroupLayout;
import javax.swing.GroupLayout.Alignment;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.border.EmptyBorder;

import gov.nasa.worldwind.WorldWindow;
import gov.nasa.worldwindx.examples.layermanager.LayerAndElevationManagerPanel;

public class LayerDialog extends JDialog
{

    private final JPanel contentPanel = new JPanel();

    /**
     * Create the dialog.
     */
    public LayerDialog(WorldWindow wwd)
    {
        setTitle("Layer Manager");
        setBounds(100, 100, 386, 360);
        getContentPane().setLayout(new BorderLayout());
        contentPanel.setBorder(new EmptyBorder(5, 5, 5, 5));
        getContentPane().add(contentPanel, BorderLayout.CENTER);
        JScrollPane scrollPane = new JScrollPane();
        scrollPane.setViewportBorder(null);
        scrollPane.add(new LayerAndElevationManagerPanel(wwd));
        GroupLayout gl_contentPanel = new GroupLayout(contentPanel);
        gl_contentPanel.setHorizontalGroup(
            gl_contentPanel.createParallelGroup(Alignment.LEADING)
                .addGroup(gl_contentPanel.createSequentialGroup()
                    .addContainerGap()
                    .addComponent(scrollPane, GroupLayout.PREFERRED_SIZE, 344, GroupLayout.PREFERRED_SIZE)
                    .addContainerGap(6, Short.MAX_VALUE))
        );
        gl_contentPanel.setVerticalGroup(
            gl_contentPanel.createParallelGroup(Alignment.LEADING)
                .addGroup(gl_contentPanel.createSequentialGroup()
                    .addContainerGap()
                    .addComponent(scrollPane, GroupLayout.DEFAULT_SIZE, 257, Short.MAX_VALUE)
                    .addContainerGap())
        );
        contentPanel.setLayout(gl_contentPanel);
        {
            JPanel buttonPane = new JPanel();
            buttonPane.setLayout(new FlowLayout(FlowLayout.RIGHT));
            getContentPane().add(buttonPane, BorderLayout.SOUTH);
            {
                JButton okButton = new JButton("OK");
                okButton.setActionCommand("OK");
                buttonPane.add(okButton);
                getRootPane().setDefaultButton(okButton);
            }
            {
                JButton cancelButton = new JButton("Cancel");
                cancelButton.setActionCommand("Cancel");
                buttonPane.add(cancelButton);
            }
        }
    }

}

Вот выдержка из MainWindow

    public MainWindow(App a)
    {

       WorldWindowGLCanvas wwd = new WorldWindowGLCanvas();

       JMenuItem mntmLayers = new JMenuItem("Layers");
       mntmLayers.addActionListener(new ActionListener()
       {
           @Override
           public void actionPerformed(ActionEvent e)
          {
               try
               {
                   LayerDialog dialog = new LayerDialog(wwd);
                   dialog.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
                   dialog.setVisible(true);
               }
               catch (Exception ex)
               {
                   ex.printStackTrace();
               }
           }
       });
    }