[Qt-interest] QGraphicsView improper widget size before resizeEvent

[franki]

Hi,

I have QGraphicsView that displays QPixmap object, and I have problem with 
resizeEvent. 
First resize causes huge change in size of QGraphicsView, the widget size 
(according to rect() function) changes much more with first resize, than it 
should be regarding the mouse move. 
Thus, when I use fitInView() function (with pixmap_item as argument) in 
resizeEvent it gives wrong size at first time, until I resize main window 
with mouse. When I do that rect() function from QGraphicsView shows this 
widget size to be about 180 pixel wider (and higher) than before resizing 
regardless how small the resize was. Why this happens?
Here is the code from constructor:

MainPages::MainPages(QWidget *parent): QStackedWidget(parent)
{
        mp.setupUi(this);
        mp.gridLayout->setContentsMargins(0,0,0,0);
        floor1_scn = new QGraphicsScene( mp.floor1_g_view );
        mp.floor1_g_view->setScene( floor1_scn );
        floor1_png=QPixmap("images/floor1.png");
        floor1_item=floor1_scn->addPixmap(floor1_png);
}
void MainPages::resizeEvent(QResizeEvent * event) {
        qDebug() << mp.floor1_g_view->rect();
        qDebug() << floor1_scn->sceneRect();
        qDebug() << floor1_item->boundingRect();
        mp.floor1_g_view->fitInView(floor1_item,Qt::KeepAspectRatio);
}

So at first time, when I run this, debug shows (before resizing):
QRect(0,0 622x462)
QRectF(-0.5,-0.5 617x463)
QRectF(-0.5,-0.5 617x463)

then after really small mouse move it shows:
QRect(0,0 784x560)
QRectF(-0.5,-0.5 617x463)
QRectF(-0.5,-0.5 617x463)

So, the size of QGraphicsView widget changes to much. It has the effect of 
dramatically changing QPixmap object during first resize event, or setting it 
to be to small before the resizeEvent, if you prefer.

The widgets are quite nested, could this be the reason? 
Hierarchy is like this: 
QMainWindow->QFrame->QStackedWidget->QTabWidget->QGgrapvicsView
and layouts between them have marigin set to zero, with 
setContentsMargins(0,0,0,0)

greetings
Marek