JComboBoxのPopupMenuを右側に表示する

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概要

JComboBoxの右側にPopupMenuが表示されるように設定します。

Screenshot

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サンプルコード

class RightPopupMenuListener implements PopupMenuListener {
  @Override public void popupMenuWillBecomeVisible(PopupMenuEvent e) {
    EventQueue.invokeLater(() -> {
      JComboBox<?> combo = (JComboBox<?>) e.getSource();
      Accessible a = combo.getAccessibleContext().getAccessibleChild(0);
      // Or Accessible a = combo.getUI().getAccessibleChild(combo, 0);
      if (a instanceof JPopupMenu) {
        JPopupMenu pop = (JPopupMenu) a;
        Point p = new Point(combo.getSize().width, 0);
        SwingUtilities.convertPointToScreen(p, combo);
        pop.setLocation(p);
      }
    });
  }

  @Override public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {
    /* not needed */
  }

  @Override public void popupMenuCanceled(PopupMenuEvent e) {
    /* not needed */
  }
}
View in GitHub: Java, Kotlin

解説

  • JComboBoxのドロップダウンリストとしてPopupMenuが開くときにその表示位置を変更するPopupMenuListenerを作成
    • JComboBox#addPopupMenuListener(...)メソッドで追加
  • JComboBoxの矢印アイコンも以下のように変更 
    combo2.setUI(new WindowsComboBoxUI() {
  @Override protected JButton createArrowButton() {
    JButton button = new JButton(icon) {
      @Override public Dimension getPreferredSize() {
        return new Dimension(14, 14);
      }
    };
    button.setRolloverIcon(makeRolloverIcon(icon));
    button.setFocusPainted(false);
    button.setContentAreaFilled(false);
    return button;
  }
});

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