[PyQt] Object lifetime issues with dialogs, called from QStyledItemDelegate editors

Barry Scott barry at barrys-emacs.org
Sun Apr 9 10:07:45 BST 2017

This has nothing to do with the problem...

I'm curious, why post on stackoverflow when you have this list with the author of the code to ask?

I see the same pattern for projects I'm the maintainer of.


> On 8 Apr 2017, at 21:06, Hans-Peter Jansen <hpj at urpla.net> wrote:
> Hi,
> I'm suffering from strange behavior related to object lifetime issues, when 
> modal dialogs are called from QStyledItemDelegate editors, and posted these 
> issues here:
> http://stackoverflow.com/questions/43298605/strange-behavior-of-qcolordialog-when-called-from-qstyleditemdelegate-subclass
> http://stackoverflow.com/questions/43299616/calling-qcolordialog-triggered-from-qstyleditemdelegate-editor-results-in-crash
> When executing the itemdelegate.py script, double clicking on a color item 
> displays the standard QColorDialog. The dialog will close immediately, if the 
> dialog is moved(!). OTOH, selecting an arbitrary color beforehand, the dialog 
> behaves correctly.. 
> The mplexitemdelegate.py script crashes, when closing the QColorDialog, after 
> being called from a QTableView subclass, triggered from a signal. 
> When started, various editors for different types appear in the second column. 
> The color editors open a QComboBox with various predefined colors. The last 
> item triggers a signal in the QTableView, that calls QColorDialog.getColor(). 
> Earlier versions attempted to open the QColorDialog from the 
> QStyledItemDelegate editor directly, similar to the code in the first issue, 
> with the same result (segfault), unlike that issue, where the QColorDialog 
> behaves strangely.
> One could observe, that opening the dialog triggers a window context change, 
> which probably results in destructing the delegate editor of the table view. 
> Therefore I implemented the selectColorDialog signal, that operates completely 
> independent from the delegate editor. The gdb backtrace points to some 
> QAccessible methods, triggered from the QComboBox, but I cannot see the 
> relation here. 
> Other attempts to cope with this issue used subclassed QComboBoxes with 
> subclassed QLineEdits, catching and ignoring any leave, hide and close events 
> during the lifetime of the color dialog, but they failed in similar ways.
> Also executing other dialogs from within this setting show the same behavior, 
> that I would like to understand.
> Any idea anybody, what's going wrong here? It might be a Qt5 issue, though.
> Thanks in advance,
> Pete
> Environment:
> Python: 3.4.5
> Sip: 4.19.2
> Qt5: 5.8.0
> PyQt5: 5.8.2
> Linux: openSUSE/KDE4<mplexitemdelegates.py><itemdelegate.py>_______________________________________________
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