How to make a ruler on the border of a QGraphicsView

Question

I am working on a small .ui project and I am was trying to understand how to properly make a ruler on a QGraphicsView.

So when the use sees th

Answer 1

On creation, scene->height() is zero by default. If ruler->setFixedHeight() unwittingly set the height of the ruler to 0, paintEvent for the ruler will not be called.

void setScene(QGraphicsScene* scene)
    {
        QGraphicsView::setScene(scene);
        if (scene)
            ruler->setFixedHeight(scene->height());
    }