How to detect TAB key-press in JComboBox?

Question

I am trying to find out how to detect if a JComboBox lost focus when user pressed tab or via a mouse-click outside the component's area.

Adding a FocusListener to the editor component of the JComboBox does not help me, as I can't find out if user used the mouse or moved the focus via the tab key. Any ideas would be greatly appreciated.

Edit 1: What I am trying to achieve is this:

• Suppose user drops down the list (JComboBox popupMenu shows up), and navigates via cursor keys...
• Case 1: user presses tab. In this case, I want to cut off some of the information from the item and show only some parts.
• Case 2: user clicks with the mouse outside the popupMenu's area (here we have subcases, but they all fall into the same category). In this case I want to change JComboBox to show the previously edited item, not what user navigated...
• There are several other cases (mouse item pick, the enter key, escape, etc.). I could easily handle these, but detecting tab is tricky because I can't catch this event as it is handled by FocusManager.

Edit 2: It seems that I have to use setFocusTraversalKeysEnabled(false) to get notified when TAB is pressed, and when i capture that event, I should manually transfer focus... I do not like this solution, but that is so far the best I could come up with.

Solution:

Following piece of Java code is actually solving my problem. As I wrote in Edit 2 the easiest solution was to disable focus traversal. I shamelessly borrowed Kleopatra's code, and all works now. :)

    if (!isTableCellEditor()) {
        comboBoxEditor.setFocusTraversalKeysEnabled(false);

        Action myAction = new AbstractAction() {

            @Override
            public void actionPerformed(ActionEvent e) {
                handleTabPress();
                comboBoxEditor.transferFocus();
            } // actionPerformed() method
        };

        comboBoxEditor.getActionMap().put("tab-action", myAction);
        comboBoxEditor.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT)
            .put(KeyStroke.getKeyStroke("TAB"), "tab-action");
    } // if

Thanks to all participants in the discussion!

Answer 1

As I understand your question, there are two separate problems

• don't commit the value while navigating
• take over the reaction to TAB

if so, the answers are

• configure the combo so that it thinks it is the editing component of a CellEditor
• disable the default traversal keys for the combo and take over with a custom binding

In code:

    final JComboBox simpleBox = new JComboBox(Locale.getAvailableLocales());
    // this line configures the combo to only commit on ENTER 
    // or selecting an item from the list
    simpleBox.putClientProperty("JComboBox.isTableCellEditor", Boolean.TRUE);
    //
    // simpleBox.setFocusTraversalKeys(KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS,
    //     Collections.EMPTY_SET);
    // just noticed the OPs edit - following indeed is easier to disable _all_ traversal
    // keys with one statement
    simpleBox.setFocusTraversalKeysEnabled(false);

    Action myAction = new AbstractAction() {

        @Override
        public void actionPerformed(ActionEvent e) {
            LOG.info("got it!");
            simpleBox.transferFocus();
        }

    };
    simpleBox.getActionMap().put("tab-action", myAction);
    simpleBox.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT)
       .put(KeyStroke.getKeyStroke("TAB"), "tab-action");