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.

Answer 1

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.

Answer 2

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.

Answer 3

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

Answer 4

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);