[Interest] How can I block the WindowActivate and FocusIn events when showing window programmatically

[John Weeks]

It's the same situation with Move and Resize events. In Qt 4, you could do this:

bool myclass::eventFilter(QObject * target, QEvent *event)
{
	static bool moving = false;

	case QEvent::move:

		// In Qt 4, the move event comes synchronously, so we know that only our call to QWidget::move
		// can cause a reentrant call here.
		if (moving)
			return;

		moving = true;
		... call QWidget::move ....
		moving = false;
}


But in Qt 5 the Move event is put on the queue and delivered asynchronously. So now I have this sort of code:

class myclass
{
	...

	private:
		bool moving;
		QWidget * movedWidget;
};

bool myclass::eventFilter(QObject * target, QEvent *event)
{
	somewidget = qobject_cast<QWidget *>(target);

	case QEvent::move:
		// in Qt 5, the call to QWidget::move doesn't cause a reentrant call here, it triggers
		// another move event later on. So we have to store away info on this call to QWidget::move,
		// and detect that move event later on when it looks like other move events.
		if (moving && somewidget == movedWidget)
		{
			moving = false;
			movedWidget = NULL;		// not at C++11 yet!
			return false;
		}

		moving = true;
		movedWidget = somewidget;
		somewidget->move();
		return <whatever>;
}

I put in a check on the widget that was moved out of paranoia that some other move event could sneek in while I was waiting. In our case, we have the same filter on multiple widgets.

Warning: I could have made some typo in the process of abstracting the method from much more complex code...

-John Weeks

On Oct 31, 2014, at 7:35 AM, Yili Pan <pyl0420 at gmail.com> wrote:

> Hi Bo:
> 
> Thank you for the reply! 
> 
> I do not want to filter out all the WindowActivate or FocusIn event tough, only these are triggered by calling QWidget::show(). But because the events are processed asynchronously in Qt5, when I catch them in the eventfilter, I don't know whether they are originated from calling show() or they are spontaneous event caused by manual interaction. I also tried to filter out the event by telling whether they are spontaneous, but unfortunately no matter where they originate from, they are spontaneous (could this be a bug??). Any thoughts or suggestion :)
> 
> Thank you!
> 
> -Yili
> 
> On Fri, Oct 31, 2014 at 4:01 AM, Bo Thorsen <bo at vikingsoft.eu> wrote:
> Den 30-10-2014 20:30, Yili Pan skrev:
> > Hi:
> >
> > We want to block the widget's WindowActivate and FocusIn event
> > triggered by calling its show() function, with Qt4,  we used to do
> > that by setting flag before and after show() and filter out the event
> > in eventfilter based on the flag.  But with Qt5, the events are
> > processed asynchronously, we cannot block the event in the same way
> > anymore.
> >
> > Any ideas how I can identify those events that are caused by calling
> > QWdiget::show() and filter them out?
> 
> You can use an event filter for this. Take a look at the documentation
> for QObject::installEventFilter, it should be simple to follow.
> 
> Bo.
> 
> --
> Viking Software
> Qt and C++ developers for hire
> http://www.vikingsoft.eu
> 
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-John