[quote=“fine”]
The Draw method doesn’t draw anything at all.[/quote]What does that mean? That means you should invoke any “TObject ::Draw” ( “TGraph::Draw” ) at once to connect the TGraph and the widget. This invocation is not causing any visual change of the widget right away.
Then you can alter your graph ( using SetPoint method, for example) as you need. As soon as you know all graph points are in you call Refresh or use any other Qt approach to “update” the Qt widget.
See doc.trolltech.com/4.7/qpaintevent.html for details. Be aware about some optimization. For example, we do not want forcing ROOT to recalculate the TObject graphical representation ( it can be the time consuming operation) as soon as “part of a widget is exposed because a covering widget was moved.”