Struggling with QGraphicsView

[HB76]

Hello there,

I'm having hard time using QGraphicsView to display images.

First, when I display an image for the first time, the image look very small despite the fact that I ask my view to fit the whole image.
In fact, I tried to display the QGraphicsView size by calling qDebug and it appeared that my QGraphicsView size was 28x28 after startup and first display, and after a second display it has been updated to the good size (wich was 800x800).

Also, I created two QPushButton to zoom in and out and I connected them with a slot that set the view scale. But when I click on the button, the view actually change but with one or more clicks of delay (not always the same).

Here is my code :

// CONSTRUCTOR
scene = new QGraphicsScene(this);
view = new GraphicsView(scene,this);
zoom_factor = 1;

...

// DRAWING SLOT
QImage image(file);
transformedScene->setSceneRect(image.rect());
transformedScene->addPixmap(QPixmap::fromImage(image));
transformedImageContainer->fitInView(scene-sceneRect(),Qt::AspectRatioMode::KeepAspectRatio);

...

// ZOOM IN AND OUT SLOTS
void window::zoomIn()
{
    zoom_factor *= 1.25;
    view->scale(zoom_factor, zoom_factor);
    view->update();
}

void PreProcessScene::zoomOut()
{
     zoom_factor *= 0.8;
     view->scale(zoom_factor, zoom_factor);
     view->update();
}

Do you know why do I get this strange behavior ?