[Interest] promoting a QGuiApplication to a QApplication?

René J.V. Bertin rjvbertin at gmail.com
Wed Jul 11 11:28:48 CEST 2018


I'm tinkering with using a Qt plugin that expects a QApplication in a QGuiApplication (specifically, a QML application using QGuiApplication).
I'm not doing anything that causes a straight crash (or haven't run into that one fatal instruction yet), but I do wonder:

is it in any way possible to promote a QGuiApplication instance to a QApplication? Somewhat unexpectedly, `dynamic_cast<QApplication*>(qApp)` behaves as `static_cast` or `const_cast` in this case (= it returns qApp). Or it returns a nullptr in

QGuiApplication app(argc, argv);
QApplication *gapp = dynamic_cast<QApplication*>(&app);

which is probably what you'd expect.

Still, with QApplication inheriting QGuiApplication one could think that the former does some initialisation the latter lacks and that it should be possible to perform those steps at a later stade. Is it?


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