How to place contextmenu in QGraphicsScene?

[Morea]

void Fraga::contextMenuEvent(QGraphicsSceneContextMenuEvent* e)
{
	QMenu menu;
	QPoint p= (mapToParent(e->scenePos())).toPoint();
	menu.addAction(_nyttsvar);
	menu.exec(   p );
}

void Fraga::contextMenuEvent(QGraphicsSceneContextMenuEvent* e)
{
	QMenu menu;
	QPoint p= (mapToParent(e->scenePos())).toPoint();
	menu.addAction(_nyttsvar);
	menu.exec(   p );
}

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Fraga is an QGraphicsRectItem. This is the code, but it doesn't seem to get maped to the correct coordinatesystem. A call to the above function places the menu outside of the Mainwindow, which is not exactly what I had hoped for.
The menu should be placed close to the mouse cursor, of course. But I don't know how.