[PyQt] why do closeEvent and destroyed slot not get called on accepting PyQt4 QDialog?

Rui DaCosta ruidc at yahoo.com
Thu Apr 7 16:27:15 BST 2011

Firstly thanks again for your reply, 

In the original code, from where this simplification is based, I have cleanup 
code on both closeEvent and destroyed, but...

that's just the problem, the closeEvent isn't getting fired (unless I manually 
call close) - except when the window is closed from the close box. 

I was expecting that from the docs for done(), I would not have to on done(), 
ie. is this a bug? or are the docs incorrect?

And separately,  destroyed is a signal according to the docs 

but I cannot get it to fire for QDialog, no matter what I do, including manually 
calling destroy(). 

The object appears deleted when inspected with sip.isdeleted, even before the 
destroy() - so if that is the case, why does it not raise a destroyed signal?

From: Demetrius Cassidy <dcassidy36 at gmail.com>
To: Rui DaCosta <ruidc at yahoo.com>
Cc: pyqt at riverbankcomputing.com
Sent: Thu, 7 April, 2011 17:02:04
Subject: Re: [PyQt] why do closeEvent and destroyed slot not get called on 
accepting PyQt4 QDialog?

I truly believe you are approaching this from the wrong angle. If you need to 
know when your QDialog is going away, you override closeEvent and do your 
cleanup from there. 

However, looking through the docs, it does not appear that destroy is actually a 
signal. It's called from the QWidget dtor, so it makes sense that if you call 
destroy(), you get the runtime error because you are deleting the C++ object 
before the Python object. Do not call destroy yourself - call self.close and 
override closeEvent. From there you can accept or reject closing the dialog, and 
do any cleanup prior to your dialog being destroyed.

From the Qt Docs:

void QWidget::destroy ( bool destroyWindow = true, bool destroySubWindows = true 
) [protected]

Frees up window system resources. Destroys the widget window if destroyWindow is 

destroy() calls itself recursively for all the child widgets, passing 
destroySubWindows for the destroyWindow parameter. To have more control over 
destruction of subwidgets, destroy subwidgets selectively first.

This function is usually called from the QWidget destructor.

On Thu, Apr 7, 2011 at 3:04 AM, Rui DaCosta <ruidc at yahoo.com> wrote:

I know it can close it manually, the problem is that this is a simplification of 
a problem I had, in which we were expecting the QDialog to close as per the 
docs, but it did not.
>The *real* problem we are facing, is a bit further down the line, where we are 
>getting the "RuntimeError: underlying C/C++ object has been deleted" but we 
>never receive a destroyed signal.
>The only reason I need this signal or event is to do some teardown code for some 
>callbacks to avoid getting this c++ error elsewhere.
From: Demetrius Cassidy <dcassidy36 at gmail.com>
>To: RuiDC <ruidc at yahoo.com>
>Sent: Thu, 7 April, 2011 0:39:33
>Subject: Re: [PyQt] why do closeEvent and destroyed slot not get called on 
>accepting PyQt4 QDialog?
>If you want to close, just call self.close. It's a slot, so you can map it to 
>any signal. Also not sure why you want to know when your widget is destroyed? 
>Let Python take care of it, you should not need to call sip.delete yourself. 
>closeEvent is there if you need to know _when_ your app was requested to close. 
>If you want to allow or reject closing the app, you need to use the QEvent 
>object which gets passed to that function. 
>On Wed, Apr 6, 2011 at 5:27 PM, RuiDC <ruidc at yahoo.com> wrote:
>>The question & code are here:
>>but hopefully someone here can give me an answer on:
>>1. how to get the closeEvent to fire from accepting (or do I have to do a
>>2. how to get the destroyed message to print (or do I have to go through
>>3. why, if I comment out the del my_widget, and uncomment the
>>my_widget.destroy() I get a:
>>RuntimeError: underlying C/C++ object has been deleted
>>on the destroy() without the print!  i.e. how is it that it can be destroyed
>>but not raise the signal?
>>Thanks in advance,
>>View this message in context: 
>>Sent from the PyQt mailing list archive at Nabble.com.
>>PyQt mailing list    PyQt at riverbankcomputing.com
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