problem with qobject_cast<QWidget *>(object) (from QML object)

[high_flyer]

because:

Returns the given object cast to type T if the object is of type T (or of a subclass); otherwise returns 0. If object is 0 then it will also return 0.

QGraphicsObject is NOT a QWidget subclass which is why:

QWidget *widget = qobject_cast<QWidget *>(object);

QWidget *widget = qobject_cast<QWidget *>(object);

To copy to clipboard, switch view to plain text mode 

wont work.

because i want a QDialog with the stuff coming from QML

This technology does not exist yet.
You can have widgets in QGraphicsView, but you can't have QGraphicsObject as QWidgets. (unless these are QProxyWidget s, which means they have a QWidget counterparts to start with)