* Subscribe/ unsubscribe listener on editor switch.
*/
@Override
protected void switchingEditors(IEditorPart previous, IEditorPart activeEditor)
{
final SearchEditor _previous = (SearchEditor) previous;
final SearchEditor _active = (SearchEditor) activeEditor;
if (_previous != null) _previous.removePropertyListener(listener);
if (_active != null) _active.addPropertyListener(listener);
}