Detect if Java Swing component has been hidden

Question

Assume we have the following Swing application:

    final JFrame frame = new JFrame();

    final JPanel outer = new JPanel();
    frame.add(outer);

    JCompon         


        

Answer 1

Thanks aioobe for your answer - I got here via Google, looking for the same thing. :-) It's worth noting that Component.isShowing() does the same job as your amIVisible() though, so a revised code snippet (including a check on the nature of the HierarchyEvent) might be:

class SomeSpecialComponent extends JComponent implements HierarchyListener {

    public void addNotify() {
        super.addNotify();
        addHierarchyListener(this);
    }

    public void removeNotify() {
        removeHierarchyListener(this);
        super.removeNotify();
    }

    public void hierarchyChanged(HierarchyEvent e) {
        if ((e.getChangeFlags() & HierarchyEvent.SHOWING_CHANGED) != 0)
            System.out.println("Am I visible? " + isShowing());
    }
}

Answer 2

Have a look at the ComponentListener (or ComponentAdapter)

http://java.sun.com/docs/books/tutorial/uiswing/events/componentlistener.html

http://docs.oracle.com/javase/8/docs/api/java/awt/event/ComponentListener.html

And specifically the method:

void componentHidden(ComponentEvent e)
    Invoked when the component has been made invisible.

A complete solution would look something like:

inner.addComponentListener(new ComponentAdapter() {
    public void componentHidden(ComponentEvent ce) {
        System.out.println("Component hidden!");
    }
});

If the actions that should be carried out upon hiding is tightly coupled with the SomeSpecialCompnent, I would suggest to let SomeSpecialComponent implement ComponentListener, and add itself as a listener for the ComponentEvents in its constructor.

Another useful way (more related to add/remove operations and perhaps not suitable for your specific scenario) is to override addNotify() and removeNotify().

Answer 3

To listen for this kind of events occuring in the hierarchy, you could do the following.

class SomeSpecialComponent extends JComponent implements HierarchyListener {

    private boolean amIVisible() {
        Container c = getParent();
        while (c != null)
            if (!c.isVisible())
                return false;
            else
                c = c.getParent();
        return true;
    }

    public void addNotify() {
        super.addNotify();
        addHierarchyListener(this);
    }

    public void removeNotify() {
        removeHierarchyListener(this);
        super.removeNotify();
    }

    public void hierarchyChanged(HierarchyEvent e) {
        System.out.println("Am I visible? " + amIVisible());
    }

}

You could even be more precise in the treatement of HierarchyEvents. Have a look at

http://java.sun.com/javase/6/docs/api/java/awt/event/HierarchyEvent.html