[prev in list] [next in list] [prev in thread] [next in thread] 

List:       pykde
Subject:    Re: [PyKDE] Issue with QDialog and lifetime
From:       James Emerton <ephelon () gmail ! com>
Date:       2005-06-23 18:45:57
Message-ID: c9424d940506231145222cd55d () mail ! gmail ! com
[Download RAW message or body]

On 6/23/05, Giovanni Bajo <rasky@develer.com> wrote:

> > Does anyone see a potential problem with exec_loop() transferring
> > ownership of the dialog instance back to Python?
> 
> Well, which C++ API would you intend to call to achieve this? We still need the
> QDialog to keep its parent widget because it is the widget on which the dialog
> is modal.

Well, the parent-child relationship still exists.  You would end up
with a bad reference if the modal dialog's parent were destroyed.  I
can't think of any correct code that would do this.  (And doing this
in C++ would cause a different set of nasty errors.)

The strategy is to tie the lifetime of the modal dialog to the Python
reference.  The ~QObject() will still clean up the parent's child
object list.  This should make the behavior equivalent to the
idiomatic C++ code.

You should be able to test this with sip.transfer( dlg, 0 ) just
before dlg.exec_loop().  Ultimately, a sipTransfer() should be added
to the %MethodCode for exec_loop().


Of course, none of this addresses the potential exeception from
MyDialog.__init__()  To do that, you would need to handle that case
explicitly.  (This is not unprecidented in C++.  If a ctor throws the
dtor is not called and the object must be manually cleaned up.)

I suppose the other option is to contaminate the public API of
QDialog.  There IS already an obsolete bool parameter, 'modal' to the
QDialog ctor that could be co-opted to mean 'don't transfer
ownership'.

James

_______________________________________________
PyKDE mailing list    PyKDE@mats.imk.fraunhofer.de
http://mats.imk.fraunhofer.de/mailman/listinfo/pykde

[prev in list] [next in list] [prev in thread] [next in thread]