[quote=“pavlovsky”]
...this->Refresh();
[/quote]
Yes, your solution is correct 
. The TQtWidget as any other QWidget is updated as soon as the " Qt system" updates the widget. For example, the user “resizes” the widget or “clicks” it.
The “Refresh” method was designed to FORCE 
Qt system to update the widget. I would like to call your attention that the Refresh is Qt slot. As such it can be connected to the suitable Qt signal.
One needs to understand how the ROOT “Draw” method works to avoid the frustration.
The Draw method doesn’t draw anything at all. See Understanding two methods: Paint() and Draw() for details