SetHorizontalScrollBar deletes the scrollbar instead of the former scrollbar and has no effect in my QGraphicsview

[korkodinos]

I have added a new Qt Designer Form Class by Template QTabWidget and in the center of it I have placed a QGraphicsview to which I would like to replace the horizontal and vertical ScrollBars with other scrollbars in my layout.

I have highlighted the QGraphicsview and scrollbars in the image below!http://tech-it.gr/Screenshot1.JPG(Layout Screenshot)!

The problem is that the following command line, instead of replacing the horizontal scroll bar with the one I have in my layout, it deletes my horizontalscrollbar.
@this->ui->graphicsView->setHorizontalScrollBar(this->ui->horizontalScrollBar);@

Could anyone tell me why could this be happening?

I have uploaded the project zip here "Your text to link here...":http://tech-it.gr/example.zip