Java Swing - Knowing if tab has been removed/added in ChangeListener

Question

Let's say I have JTabbedPane with a ChangeListener

JTabbedPane tabbedPane = new JTabbedPane();

// Add few tabs
.....
.....

tabbedPane.addChangeListener(new ChangeListener() {
  public void stateChanged(ChangeEvent changeEvent) {
    // How to determine if the changeEvent was fired because of a tab remove/add ?
  }
});

and somewhere I am doing a

tabbedPane.removeTabAt(2);

and somewhere else

tabbedPane.add(panel, 0);

The ChangeListener should get fired now, is there any way to determine within the listener if it was called due to a tab remove/add ?

EDIT: I am basically trying to do some actions only when the user switches between tabs and not when adding or removing.

Can you elaborate on how the action should respond differently. — trashgod, Aug 20 '12 at 11:47
There is a combobox outside the tabbedPane which needs to be modified only when the user switches between tabs and a change in the combobox can in turn add/remove tabs! — Krishnaraj, Aug 20 '12 at 11:57
hmm ... so it _is_ related to the tab component, that is the combo would need to be updated when the selected tab is removed? — kleopatra, Aug 20 '12 at 12:00
yes but the combo need not be updated when the tab is added back — Krishnaraj, Aug 20 '12 at 12:09
adding it back doesn't change the selected _component_ - as long as you have no custom logic which auto-selects the added - so my solution should work fine. If not, please add an SSCCE to demonstrate your exact context — kleopatra, Aug 20 '12 at 12:56

score 7 · Answer 1 · edited Aug 20 '12 at 11:16

7

If I remember correctly, JTabbedPane will fire a componentAdded() event (defined in Container) when a new tab is added and a componentRemoved() event if a tab is removed.

You should be able to listen for adding or removal of a tab by registering a ContainerListener

http://docs.oracle.com/javase/7/docs/api/java/awt/Container.html#addContainerListener(java.awt.event.ContainerListener)

The stateChanged() event is just a side-effect of the add because the JTabbedPanel automatically switches to the new tab.

edited Aug 20 '12 at 11:16

nIcE cOw

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answered Aug 20 '12 at 11:10

missed out what I am actually trying to do, please check out my edit – Krishnaraj Aug 20 '12 at 11:17

score 2 · Answer 2 · answered Aug 20 '12 at 11:18

2

You might also want to examine the client property __index_to_remove__, which is set by removeTabAt().

answered Aug 20 '12 at 11:18

trashgod

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2

hmm ... doesn't help when adding a tab, afaics? – kleopatra Aug 20 '12 at 11:33
@kleopatra: Good point; I also missed the update to the question. Adding a similar property to the `addTabAt()` methods seems awkward. Requesting clarification above. – trashgod Aug 20 '12 at 11:48

score 2 · Accepted Answer · answered Aug 20 '12 at 11:51

2

Depending on the exact requirement, you might keep track of the selected component and only do stuff if that has changed:

ChangeListener l = new ChangeListener() {

    Component lastSelected = tabbedPane.getSelectedComponent();
    @Override
    public void stateChanged(ChangeEvent e) {
        if (lastSelected != tabbedPane.getSelectedComponent()) {
            LOG.info("changed: " + tabbedPane.getSelectedIndex());
            lastSelected = tabbedPane.getSelectedComponent();
        }

    }
};
tabbedPane.addChangeListener(l);

Might not be good enough, though, as it will trigger if the selected tab itself is removed.

answered Aug 20 '12 at 11:51

kleopatra

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+1 I don't see an easier way. I notice that `fireStateChanged()` occurs `if (index == selected)`. – trashgod Aug 20 '12 at 11:56
having a flag to keep track of all add/remove operations seems to be the only reliable way :(. Really surprised that ChangeEvent doesn't have any state information. This should be a common problem, ain't it? – Krishnaraj Aug 21 '12 at 06:12
accepting this answer as this could be good enough for many ppl – Krishnaraj Aug 21 '12 at 06:12

score 0 · Answer 4 · answered Jan 07 '14 at 22:00

By keeping track of the current number of tabs, you can detect a selection change based on add or delete

ChangeListener l = new ChangeListener() {

    int lastTabCount = tabbedPane.getTabCount();
    Component lastSelected = tabbedPane.getSelectedComponent();

    @Override
    public void stateChanged(ChangeEvent e) {
        if (lastSelected != tabbedPane.getSelectedIndex())
        {
            int currentTabCount = tabbedPane.getTabCount();
            if (lastTabCount == currentTabCount ) {
                LOG.info("changed: " + tabbedPane.getSelectedIndex());
            } else if (lastTabCount < currentTabCount)
                LOG.info("changed due to delete: " + tabbedPane.getSelectedIndex());
            } else if (lastTabCount > currentTabCount)
                LOG.info("changed due to add: " + tabbedPane.getSelectedIndex());
            }
            lastTabCount = tabbedPane.getTabCount();
            lastSelected = tabbedPane.getSelectedComponent();
        }

    }
};
tabbedPane.addChangeListener(l);

Java Swing - Knowing if tab has been removed/added in ChangeListener

4 Answers4