void QGraphicsScenePrivate::_q_polishItems()
{
    const QVariant booleanTrueVariant(true);
    QList<QGraphicsItem*> items = unpolishedItems;
    unpolishedItems.clear();

    int count(items.count());
    while (count--) {
        QGraphicsItem *item = items.at(count);
        if (!item->d_ptr->explicitlyHidden) {
            item->itemChange(QGraphicsItem::ItemVisibleChange, booleanTrueVariant);
            item->itemChange(QGraphicsItem::ItemVisibleHasChanged, booleanTrueVariant);
        }
        if (item->isWidget()) {
            QEvent event(QEvent::Polish);
            QApplication::sendEvent((QGraphicsWidget *)item, &event);
        }
    }
}

#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsWidget>
#include <QGraphicsView>

class RectWidget : public QGraphicsWidget
{
public:

    RectWidget(Qt::GlobalColor color, QGraphicsItem *parent=0) : 
    QGraphicsWidget(parent), mColor(color)
    {
    }

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *) 
    {
        painter->setBrush(QBrush(mColor));
        painter->drawRect(boundingRect());
    }

    void polishEvent()
    {
        QGraphicsWidget::polishEvent();
        mColor = Qt::red;
        update();
    }

    void resizeEvent(QGraphicsSceneResizeEvent *event)
    {
        QGraphicsWidget::resizeEvent(event);
        
        if (!parentWidget()) {
            RectWidget *childWidget = new RectWidget(Qt::black, this);
            childWidget->setGeometry(QRectF(10,10,30,30));
        }
    }

private:

    Qt::GlobalColor mColor;
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QGraphicsScene scene;

    RectWidget *parentWidget = new RectWidget(Qt::white);
    scene.addItem(parentWidget);

    QGraphicsView view(&scene);
    view.resize(200, 200);
    view.show();

    return app.exec();
}