QApplication can’t be receiver of its own signal aboutToExit?

I got some cleanup job before app exit, by following document, I built my own QMyApplication with a private slot cleanup() and got it connected to aboutToExit signal.

However, I found cleanup() was never called.

Then I added another class QMyApplicationHelper (definitely inherited from QObject) to receive aboutToExit instead. That worked.

I was wondering if QApplication can’t be receiver of its own signal aboutToExit.

Furthermore, I also tried an idle processing by use of a QTimer with 0 timeout, like

It still never worked until I had QMyApplicationHelper be receiver of timer.

I didn’t figure out why there has to be a helper class to take over role of signal receiver.

Thx.

[EDIT: code highlighting, Volker]