Is there a way to get notification when JComponent is not visible anymore beucase parent is removed from collection?

Question

Say I have a simple JFrame with a JTabbedPane containing 3 panels, and the second panel contains a JComponent. Is there a way the JComponent to be notified when "Tab 2" panel is removed from its container? My problem is that the JComponent may be deep in the hierarchy.

Obviously, I am looking for SWING solution here... :)

 ,'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''`.
 |                                                                |
 | ,----------Y.......................                            |
 | | Tab 1    | Tab 2     | Tab 3    |                            |
 | :..........:           :.....................................  |
 | |                                                           |  |
 | |                                                           |  |
 | |                                                           |  |
 | |               +--------------------+                      |  |
 | |               |Some JComponent here|                      |  |
 | |               +--------------------+                      |  |
 | |                                                           |  |
 | |                                                           |  |
 | |                                                           |  |
 | |                                                           |  |
 | |                                                           |  |
 | |                                                           |  |
 | |                                                           |  |
 | |                                                           |  |
 | |                                                           |  |
 | |                                                           |  |
 | `-----------------------------------------------------------'  |
 `-----------------------------------------------------------------

I tried to do this with the ancestorRemoved(), but no luck... I am obviously doing something wrong...

PS. the ASCII art is made with JavE.

Answer 1

I'd be use ComponentListener for this job (CardLayout is so close, similar in compare with JTabbedPane), code example contains all related listeners (disclaimer --> notice blocking EDT works only as code example and in this form only)

Ancesor & HierarchyListener are little bit asynchronous, maybe there is your problem to catch proper event from AncestorListener

my question about similar issue

import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.event.HierarchyEvent;
import java.awt.event.HierarchyListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.event.AncestorEvent;
import javax.swing.event.AncestorListener;

public class CardlayoutTest extends JFrame {

    private static final long serialVersionUID = 1L;
    public CardLayout card = new CardLayout();

    public CardlayoutTest() {
        JPanel pnlA = new JPanel(new BorderLayout());
        pnlA.add(new JButton("A"), BorderLayout.CENTER);
        JPanel pnlB = new JPanel(new BorderLayout());
        pnlB.add(new JButton("B"), BorderLayout.CENTER);
        JPanel pnlC = new JPanel(new BorderLayout());
        pnlC.add(new JButton("C"), BorderLayout.CENTER);

        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLayout(card);
        add(pnlA, "A");
        add(pnlB, "B");
        add(pnlC, "C");

        pnlA.addAncestorListener(new EventHandler());
        pnlB.addAncestorListener(new EventHandler());
        pnlC.addAncestorListener(new EventHandler());

        pnlA.addHierarchyListener(new EventHandler());
        pnlB.addHierarchyListener(new EventHandler());
        pnlB.addHierarchyListener(new EventHandler());

        pnlA.addComponentListener(new EventHandler());
        pnlB.addComponentListener(new EventHandler());
        pnlB.addComponentListener(new EventHandler());
    }

    class EventHandler implements AncestorListener, ComponentListener, HierarchyListener {

        @Override
        public void ancestorAdded(AncestorEvent event) {
            System.out.println("CardlayoutTest.EventHandler.ancestorAdded()");
        }

        @Override
        public void ancestorMoved(AncestorEvent event) {
            System.out.println("CardlayoutTest.EventHandler.ancestorMoved()");
        }

        @Override
        public void ancestorRemoved(AncestorEvent event) {
            System.out.println("CardlayoutTest.EventHandler.ancestorRemoved()");
        }

        @Override
        public void hierarchyChanged(HierarchyEvent e) {
            System.out.println("Components Change: " + e.getChanged());
            if ((e.getChangeFlags() & HierarchyEvent.DISPLAYABILITY_CHANGED) != 0) {
                if (e.getComponent().isDisplayable()) {
                    System.out.println("Components DISPLAYABILITY_CHANGED : " + e.getChanged());
                } else {
                    System.out.println("Components DISPLAYABILITY_CHANGED : " + e.getChanged());
                }
            }
            if ((e.getChangeFlags() & HierarchyEvent.SHOWING_CHANGED) != 0) {
                if (e.getComponent().isDisplayable()) {
                    System.out.println("Components SHOWING_CHANGED : " + e.getChanged());
                } else {
                    System.out.println("Components SHOWING_CHANGED : " + e.getChanged());
                }
            }
        }

        public void componentHidden(ComponentEvent e) {
            System.out.println(e.getComponent().getClass().getName() + " --- Hidden");
        }

        public void componentMoved(ComponentEvent e) {
            System.out.println(e.getComponent().getClass().getName() + " --- Moved");
        }

        public void componentResized(ComponentEvent e) {
            System.out.println(e.getComponent().getClass().getName() + " --- Resized ");
        }

        public void componentShown(ComponentEvent e) {
            System.out.println(e.getComponent().getClass().getName() + " --- Shown");
        }
    }

    public static void main(String[] args) {
        CardlayoutTest t = new CardlayoutTest();
        t.setSize(500, 500);
        System.out.println("CardlayoutTest.main()------------------------ FIRST");
        t.card.show(t.getContentPane(), "A");
        t.setVisible(true);
        System.out.print("\n");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println("CardlayoutTest.main()------------------------ SECOND");
        t.card.show(t.getContentPane(), "B");
        System.out.print("\n");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println("CardlayoutTest.main()------------------------ THIRD");
        t.card.show(t.getContentPane(), "C");
        System.out.print("\n");
    }
}

Answer 2

If it is the component itself which needs to do something, you can also override add/removeNotify (don't forget to call super though.

import java.awt.*;
import java.awt.event.*;
import java.util.Date;
import javax.swing.*;

public class LabelWithTimer extends JLabel {

    private final Timer timer;

    public LabelWithTimer() {
        timer = new Timer(1000, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                setText(new Date().toString());
            }
        });
    }

    @Override
    public void addNotify() {
        super.addNotify();
        timer.start();
        System.out.println("Clock started");
    }

    @Override
    public void removeNotify() {
        System.out.println("Clock stopped");
        timer.stop();
        super.removeNotify();
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                final JPanel clock = new JPanel(new GridBagLayout());
                clock.add(new LabelWithTimer());

                final JTabbedPane tabs = new JTabbedPane();
                tabs.addTab("Empty", new JLabel());
                tabs.setPreferredSize(new Dimension(400, 300));

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                frame.getContentPane().add(tabs);
                frame.getContentPane().add(new JButton(new AbstractAction("Add/remove clock") {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        if(tabs.getTabCount() == 2) {
                            tabs.removeTabAt(1);
                        }
                        else {
                            tabs.addTab("Clock", clock);
                            tabs.setSelectedIndex(1);
                        }

                    }
                }), BorderLayout.PAGE_END);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}