// Returns a use-selected-observation-checkbox listener.
private ActionListener createUseSelectedObservationCheckBoxHandler() {
return new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
ObservationSelectionMessage selMsg = null;
// If the checkbox is selected, retrieve the last selected
// observation from the current view. This of course could be
// null, except that this checkbox is only enabled when an
// observation *has* been selected, so it really *can't* be null