How to capture the QDockWidget close button click event

I have a QStackedWidget within a QDockWidget - depending on which page is shown I wish to show/hide the close button on the QDockWidget. I can do this by using QDockWidget::setFeatures().

However the issue I'm facing is how to capture the signal of the close button so that I can change the dock features / set the stacked widget page index.

I have attempted to use an event filter:

class EventFilter : public QObject
{
    Q_OBJECT
public:
    EventFilter( QObject* aParent );
protected:
    bool eventFilter(QObject *obj, QEvent *event);
};

EventFilter::EventFilter( QObject* aParent )
    : QObject( aParent )
{

}

bool EventFilter::eventFilter( QObject *obj, QEvent *event )
{
    if ( event->type() == QEvent::Close )
    {
        return true;
    }
    return QObject::eventFilter( obj, event );
}

And installed it as so:

EventFilter* filter = new EventFilter( this );
u->dockWidget_6->installEventFilter( filter );

In the constructor of my QMainWindow - the eventFilter() method did not get called.

So next I attempted to use the QDockWidget::visibilityChanged changed signal since it sounded like this might be what I wanted:

connect( u->dockWidget_6, SIGNAL(visibilityChanged(bool)), SLOT(dockWindowClosed(bool)) );

This slot did get called - but not when the close button was clicked.

Finally I attempted to use a promoted QDockWidget to capture the QWidget::closeEvent().

  class DockWidgetWithCloseSignal : public QDockWidget
  {
       Q_OBJECT
   public:
      explicit DockWidgetWithCloseSignal(const QString &title, QWidget *parent = 0, Qt::WindowFlags flags = 0)
        : QDockWidget( title, parent, flags )