recognise combobox deselect when using Swing + models?

Question

I'm trying to write a nice GUI in Swing that uses the proper Model-Delegate pattern as much as possible. I have a JComboBox that when changed, needs to update the model with the new data. To get the currently selected item, I am using:

fooCombo.addItemListener(new ItemListener() {
    public void itemStateChanged(final ItemEvent arg0) {
        fooChangedHandler((Foo) fooModel.getSelectedItem());
    }
});

Which returns what the data was changed to as a nice Object. However, I can't find a way to find out the old value, so I don't know which object needs to be changed. Any ideas here?

Answer 1

As the default ComboBoxModel and ItemEvent does not let you get the previously selected value you could implement your own ComboBoxModel with this feature.

Answer 2

Foo oldFoo;
....
fooCombo.addItemListener(new ItemListener() {
    public void itemStateChanged(final ItemEvent arg0) {
        Foo newFoo = (Foo) fooModel.getSelectedItem();
        fooChangedHandler(oldFoo, newFoo);
        oldFoo = newFoo;
    }
});

Answer 3

ended up not going to the model at all but getting my object from the getItem method like so:

public void itemStateChanged(final ItemEvent event) {
    if (event.getStateChange() == event.DESELECTED) {
        deselectedFoo = (Foo) event.getItem();
    } 
    else if (event.getStateChange() == event.SELECTED) {
        FooChangedHandler(deselectedFoo,(Foo) event.getItem());
    }
}