Parented QGraphicsView won't receive events

RedWark

I've made some tests on Graphics and stumble upon an issue that I can't figure out. To sum up, I have a different behavior for the same QGraphicsView when it's parented or not.

Here is the problem, I have a simple subclass of a QGraphicsView which is like this:

@#ifndef GRAPHICS_VIEW_H
#define GRAPHICS_VIEW_H

#include <QGraphicsView>

class QTimer;

class GraphicsView: public QGraphicsView
{
Q_OBJECT
public:
explicit GraphicsView(QWidget *parent = 0);

protected:
virtual void paintEvent(QPaintEvent* event);

private:
QTimer* a_timer;

};

#endif // GRAPHICS_VIEW_H
@

And the implementation:

@#include "graphics_view.h"

#include <QDebug>
#include <QTimer>

GraphicsView::GraphicsView(QWidget* parent)
: QGraphicsView(parent)
{
setFrameStyle(QFrame::NoFrame);
setLineWidth(0);
a_timer = new QTimer(this);
connect(a_timer, SIGNAL(timeout()), this, SLOT(update()));
a_timer->start(50);
}

void GraphicsView::paintEvent(QPaintEvent* event)
{
qDebug() << "CustomWidget::paintEvent";
QGraphicsView::paintEvent(event);
}
@

If I instantiate it directly in a main like this:

@int main(int argv, char *args)
{
QApplication app(argv, args);
GraphicsView widget = new GraphicsView();
widget->show();
return app.exec();
}@

Everything works fine and I've the following output:

@CustomWidget::paintEvent
CustomWidget::paintEvent
CustomWidget::paintEvent
@

Repeated every 50 ms.

But, if I embed it in a parent widget like this one:

@#ifndef PARENT_WIDGET_H
#define PARENT_WIDGET_H

#include <QWidget>

class GraphicsView;

class ParentWidget : public QWidget
{
Q_OBJECT
public:
explicit ParentWidget(QWidget *parent = 0);
void showMe();

private:
GraphicsView* a_widget;

};

#endif // PARENT_WIDGET_H
@

And the implementation:

@#include "parent_widget.h"
#include "graphics_view.h"

#include <QDebug>

ParentWidget::ParentWidget(QWidget *parent): QWidget(parent)
{
a_widget = new GraphicsView(this);
}

void ParentWidget::showMe()
{
show();
a_widget->show();
}
@

And I try to use it via this main:
@
int main(int argv, char **args)
{
QApplication app(argv, args);
ParentWidget papaWidget;
papaWidget.showMe();
return app.exec();
}@

Then I have no output. Also changing the parent of ParentWidget::a_widget from this to NULL in ParentWidget constructor solves the issue but then I have two windows open (which is normal).

I also verified that if I derived GraphicsView from QWidget rather than QGraphicsView then GraphicsView::paintEvent() gest called.

So how can I parent a QGraphicsView and still update it via the event loop? It must be obvious but I just can't see what's wrong here.

Thanks.