QPainter::begin:: A paint device can only be painted by one painter at a time

[wone]

Hello. I am a very very beginner.
There is a very big problem with using Qpainter. I keep getting the following error in my project.
"QPainter::begin:: A paint device can only be painted by one painter at a time"
So I tried running another project that was running fine on another computer to try it out, but still got the same error at that perfect project. So I created a new widget project and executed it without adding anything other than the above sentence, but I still get the same error. Obviously, Qpainter was used only in one place, but why does this error occur?
I think there are other problems in my environment because I see the same error even on a project that runs well on another computer, but I don't know what it is....
Please save me ,,,,,,,,,,,,,,

[Bonnie]

As I can see, the QImage has not be created, it is a wild pointer.
It surprises me that you didn't get a crash.

[JonB]

@wone
Not only is @Bonnie correct, I can also see a yellow warning triangle against your painter.begin(img) line. What does that warning tell you?