[PyQt] QWidget 'destroyed' signal: possible regression?

Phil Thompson phil at riverbankcomputing.com
Sun Mar 11 11:05:07 GMT 2012

On Sun, 11 Mar 2012 11:48:44 +0100, Erik Janssens
<Erik.Janssens at conceptive.be> wrote:
> Hello Pierre, Phil,
> I'm not so sure the current behavior is inconsistent.  One
> of the reasons of using signal/slot over normal callbacks is
> that they are disconnected when one of the objects gets
> deleted.
> So if you connect the destroyed signal to a non-QObject-method, the
> slot is called.  If you connect it to a QObject-method that has
> been deleted, the slot is not called.  

Yes - but the point is that it hasn't yet been deleted.

> The destroyed signal is emitted in the destructor of QObject.  So in
> case of a QWidget, this after the QWidget destructor has done its work.
> After this has been done, any call to a QWidget method might crash the
> application.
> I would prefer the behavior to be consistent with C++ Qt (although
> I don't know what that exactly is)

I think the (now changed) behaviour is consistent.

> The documentation of Qt states that the destroyed signal should be
> used to monitor a QObject, I don't think its intended to serve
> as a kind of destructor.

Agreed - which is why I said I considered this particular usage an
application bug.

> It's worth thinking this through before changing it...

It's been changed - but it can always be changed back if current snapshots
prove to be a problem.


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