Move QGraphicsScene by mouse

HI!

I want to move a scene with mouse (left mouse button with CTRL). I use this code:

Code:

void GraphicsView::mousePressEvent (QMouseEvent *event)
{
    if (event->button () == Qt::LeftButton && event->modifiers ().testFlag (Qt::ControlModifier))
    {
        setDragMode (QGraphicsView::ScrollHandDrag);
        setInteractive (false);
 
        _originX = event->x ();
        _originY = event->y ();
    }
    else
    {
        QGraphicsView::mousePressEvent (event);
    }
}
 
void GraphicsView::mouseMoveEvent (QMouseEvent *event)
{
    if (event->buttons () & Qt::LeftButton && event->modifiers ().testFlag (Qt::ControlModifier))
    {
        QPointF oldp = mapToScene (_originX, _originY);
        QPointF newp = mapToScene (event->pos ());
        QPointF translation = newp - oldp;
 
        translate (translation.x (), translation.y ());
 
        _originX = event->x ();
        _originY = event->y ();
        return;
    }
 
    QGraphicsView::mouseMoveEvent (event);
}
 
void GraphicsView::mouseReleaseEvent (QMouseEvent *event)
{
    if (event->button () == Qt::LeftButton && event->modifiers ().testFlag (Qt::ControlModifier))
    {
        setDragMode (QGraphicsView::NoDrag);
        setInteractive (true);
    }
    else
    {
        QGraphicsView::mouseReleaseEvent (event);
    }
}

And this code is not work.