Change the height of a drop-down list of JComboBox by mouse dragging

• download example.jar
• download src.zip
• repository

Code

JPopupMenu popup = new JPopupMenu();
popup.setBorder(BorderFactory.createEmptyBorder());
popup.setPopupSize(240, 120);

JLabel bottom = new JLabel("", new DotIcon(), SwingConstants.CENTER);
MouseInputListener rwl = new ResizeWindowListener(popup);
bottom.addMouseListener(rwl);
bottom.addMouseMotionListener(rwl);
bottom.setCursor(Cursor.getPredefinedCursor(Cursor.S_RESIZE_CURSOR));
bottom.setOpaque(true);
bottom.setBackground(new Color(0xE0_E0_E0));
bottom.setFocusable(false);

JPanel resizePanel = new JPanel(new BorderLayout());
resizePanel.add(scroll);
resizePanel.add(bottom, BorderLayout.SOUTH);
resizePanel.add(Box.createHorizontalStrut(240), BorderLayout.NORTH);
resizePanel.setBorder(BorderFactory.createLineBorder(new Color(0x64_64_64)));

JPopupMenu popup = new JPopupMenu();
popup.add(resizePanel);

// ...
class ResizeWindowListener extends MouseInputAdapter {
  private final Rectangle rect = new Rectangle();
  private final JPopupMenu popup;
  private final Point startPt = new Point();
  private final Dimension startDim = new Dimension();

  protected ResizeWindowListener(JPopupMenu popup) {
    this.popup = popup;
  }

  @Override public void mousePressed(MouseEvent e) {
    rect.setSize(popup.getSize());
    startDim.setSize(popup.getSize());
    startPt.setLocation(e.getComponent().getLocationOnScreen());
  }

  @Override public void mouseDragged(MouseEvent e) {
    rect.height = startDim.height + e.getLocationOnScreen().y - startPt.y;
    popup.setPreferredSize(rect.getSize());
    Window w = SwingUtilities.getWindowAncestor(popup);
    if (w != null && w.getType() == Window.Type.POPUP) {
      // Popup$HeavyWeightWindow
      w.setSize(rect.width, rect.height);
    } else {
      // Popup$LightWeightWindow
      popup.pack();
    }
  }
}

References

• Change the height of a drop-down list of JComboBox by mouse dragging(Japanese)