Deleting object after QQmlEngine quit. How?

bogong

Hello all!
I have an issue with application quit process.
The object ABackend that is created like this:

int main(int inCounter, char* inArguments[]) {

#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
	QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif

	QGuiApplication oApplication(inCounter, inArguments);
	QQmlApplicationEngine oEngine;

	qInstallMessageHandler(fLoggerMessageHandler);

	ABackend* oBackend = &ABackend::mInstance();

	oBackend->pGuiApplication = &oApplication;
	oBackend->pEngine = &oEngine;
	oBackend->pRootContext = oEngine.rootContext();

	oBackend->mInit();

	const QUrl oURL(QStringLiteral(SCOUT_QML_MAIN));
	QObject::connect(
		&oEngine, &QQmlApplicationEngine::objectCreated,
		&oApplication, [oURL](QObject *obj, const QUrl &objUrl) {
			if (!obj && oURL == objUrl) {
				QCoreApplication::exit(-1);
			}
		}, Qt::QueuedConnection
	);
	oEngine.load(oURL);

	return oApplication.exec();

is deleting faster than QML engine quit properly. And result of it I see this message:

TypeError: Cannot call method 'mSomeMethodOfAbackend' of null

The question is how to delete it only after QML Engine destruction?

sierdzio

Either move this line:

ABackend* oBackend = &ABackend::mInstance();

Before this:

QQmlApplicationEngine oEngine;

Or (better) parent oBackend under oEngine. You'll need to expose it's constructor, then do it like so:

auto oBackend = new ABackend(&oEngine);

bogong

@sierdzio Just it? I though there would be something very complicated related to Signal-Slots ... I am definitely in need of getting rest ... Started forgetting how objets parenting in Qt. Thx. Issue closed.

sierdzio

Yeah, this started appearing a few versions ago, around 5.13 or 5.14. I think some bug fix must have changed QQmlEngine destructor or something. In every case I noticed these TypeError logs, it was enough to change parenting or initialization order to fix the issue.