QGraphicsView in a QDialog?

[tbscope]

This is so very very wrong :-)

ui->view->setScene(&scene);
ui->view->show();

ui->view->setScene(&scene);
ui->view->show();

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Among other lines, this will at least put your paint event in an infinite loop.

And from what it looks like, you don't even need to use the paint event of your dialog.
Why use a graphics view and start painting yourself?

The only thing and nothing else you should be doing in the paint event is painting.