JComboBox自定義單元格渲染器-如何獲取組合的isEnabled（）狀態？

有點棘手，但可能；）

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.Graphics;
import java.util.function.Predicate;

import javax.annotation.Nullable;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPopupMenu;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import javax.swing.plaf.basic.BasicComboBoxRenderer;

/**
 * <code>ComboTest</code>.
 */
public class ComboTest {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new ComboTest()::startUp);
    }

    private void startUp() {
        JFrame frm = new JFrame("Combo test");
        JComboBox<String> combo = new JComboBox<>(new String[] {"One", "Two", "Three"});
        combo.setRenderer(new EnablementCellRenderer());
        JButton b = new JButton("Toggle Enabled");
        b.addActionListener(l -> {
            combo.setEnabled(!combo.isEnabled());
            combo.repaint();
        });
        frm.add(combo);
        frm.add(b, BorderLayout.EAST);
        frm.pack();
        frm.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frm.setLocationRelativeTo(null);
        frm.setVisible(true);
    }

    private class EnablementCellRenderer extends BasicComboBoxRenderer {

        @Override
        protected void paintComponent(Graphics g) {
            JComboBox<?> combo = getFirstAncestorOfClass(this, JComboBox.class);
            setForeground(combo.isEnabled() ? Color.BLUE : Color.GREEN);
            super.paintComponent(g);
        }
    }

    /**
     * Searches for the first ancestor of the given component which is the instance of the given class.
     *
     * @param aStart start component to search. If the component is instance of the class - it will be returned.
     * @param condition condition used to determine the component.
     * @return first ancestor of the given component which is the instance of the given class. Null if no such component found.
     */
    @Nullable
    public static Container getFirstAncestor(Component aStart, Predicate<Component> condition) {
        Container result = null;
        Component base = aStart;
        while ((result == null) && (base.getParent() != null || getInvoker(base) != null)) {
            base = getInvoker(base) == null ? base.getParent() : getInvoker(base);

            result = condition.test(base) ? (Container) base : null;
        }
        return result;
    }

    /**
     * Searches for the first ancestor of the given component which is the instance of the given class.
     *
     * @param aStart start component to search. If the component is instance of the class - it will be returned.
     * @param aClass class of component.
     * @return first ancestor of the given component which is the instance of the given class. Null if no such component found.
     * @param <E> class of component.
     */
    @Nullable
    public static <E> E getFirstAncestorOfClass(Component aStart, Class<E> aClass) {
        return aClass.cast(getFirstAncestor(aStart, aClass::isInstance));
    }

    /**
     * Gets the invoker of the given component when it's a pop-up menu.
     *
     * @param c component which invoker must be found.
     * @return the invoker when the given component is a pop-up menu or null otherwise.
     */
    private static Component getInvoker(Component c) {
        return c instanceof JPopupMenu ? ((JPopupMenu) c).getInvoker() : null;
    }

}