(Qt 4.8) QScrollBar::isVisible not updating after calling QGraphicsView::scale

Code:

---

void GraphicsView::zoom(qreal s){
    scale(s, s);
    zoomLevel *= s;
}
 
void GraphicsView::zoomToWidth(){
    zoom((qreal)width() / (scene->sceneRect().width() * zoomLevel)); //this causes both scroll bars to appear
 
    if(horizontalScrollBar()->isVisible() && verticalScrollBar()->isVisible()){
        //...
    }
}

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But the if statement doesn't run, even though both scroll bars are visible. If I then immediately run zoomToWidth again, the if statement does run, so it seems like the scroll bars aren't being "updated" immediately. Is there a way to fix this?