Dock widget not visible

[Perdrix]

I have a dock widget that's owned by a QDialog that may not be visible under all circumstances when the application is closed and the window state is saved.

When I restart I want to show this dialog and the dock widget.

So in onInitialise() that I call from here:

void DeepSkyStacker::showEvent(QShowEvent* event)
{
	// Invoke base class showEvent()
	Inherited::showEvent(event);
	if (!event->spontaneous())
	{
		if (!initialised)
		{
			initialised = true;
			onInitialise();
		}
	}
}

I wrote:

	stackingDlg->setVisible(true);
	setTab(IDD_REGISTERING);
	update();

which in turn called code that did this:

	stackedWidget->setCurrentIndex(0);
	stackingDlg->showImageList();
	stackingDlg->update();

where the call to stackingDlg->showImageList() calls setVisible(true) for the dock widget.

Problem is that it didn't work :(

In the end, in a fit of desperation, I changed the code in onInitialise() to read:

	QTimer::singleShot(20,
		[this]()
		{
			this->stackingDlg->setVisible(true);
			this->setTab(IDD_REGISTERING);
			this->update();
		});

and lo it all works as I expect.

Please can someone explain why I needed to put that code into a single shot?

[Perdrix]

@Perdrix I got round that ugly hack by making the dock widget in question visible as the application was closing (in the closeEvent handler).

Still don't understand why that "One Shot" was needed though.