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。

RightPopupMenuComboBox.png

サンプルコード

class RightPopupMenuListener implements PopupMenuListener {
  @Override public void popupMenuWillBecomeVisible(final PopupMenuEvent e) {
    EventQueue.invokeLater(new Runnable() {
      @Override public void run() {
        JComboBox combo = (JComboBox) e.getSource();
        Accessible a = combo.getUI().getAccessibleChild(combo, 0);
        if (a instanceof BasicComboPopup) {
          BasicComboPopup pop = (BasicComboPopup) a;
          Point p = new Point(combo.getSize().width, 0);
          SwingUtilities.convertPointToScreen(p, combo);
          pop.setLocation(p);
        }
      }
    });
  }
  @Override public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {}
  @Override public void popupMenuCanceled(PopupMenuEvent e) {}
}
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解説

  • JComboBoxのドロップダウンリストとしてPopupMenuが開くとき、その位置を変更する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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