Thank you very much for your help!
I'm going to make a research about "queued signal/slot connection instead of
direct connection" since that is completely new for me :-)
Meanwhile, now that I know the reason of the error, my workaround consists in
delaying the handling of the feature addition using the editCommandEnded slot.
This is the relevant code:
def onFeatureAdded(self, fid):
if fid < 0:
self._addedFeatures.append(fid)
def onEditCommandEnded(self):
while self._addedFeatures:
fid = self._addedFeatures.pop()
self._handleAdded(fid)
def _handleAdded(self, fid):
guid_pol = str(uuid4()) # RFC 4122 UUID v4
try:
self.layer.beginEditCommand(u"Assign UUID")
self.layer.changeAttributeValue(fid,
self.layer.fieldNameIndex('guid_pol'), guid_pol)
self.layer.endEditCommand()
except:
self.layer.destroyEditCommand()
raise
So far seems to work.
-----Mensaje original-----
De: Martin Dobias [mailto:wonder...@gmail.com]
Enviado el: domingo, 06 de marzo de 2016 9:53
Para: Manuel Hernández Martínez
CC: Qgis-developer@lists.osgeo.org
Asunto: Re: [Qgis-developer] QGIS crashes when doing a rollback after modifying
values of an user-added feature with pyQGIS
Hi Manuel
On Fri, Mar 4, 2016 at 10:05 PM, Manuel Hernández Martínez
<mhernand...@agenciamedioambienteyagua.es> wrote:
>
> self.iface.mapCanvas().currentLayer().featureAdded.connect(self._debug
> _onFeatureAdded)
>
> def _debug_onFeatureAdded(self, fid):
> layer = self.iface.mapCanvas().currentLayer()
> layer.beginEditCommand("Set UUID")
> print layer.changeAttributeValue(fid,
> layer.fieldNameIndex('guid_pol'), 'some_random_uuid') # prints True
> layer.endEditCommand()
>
> [...]
>
> When I edit the layer, if I add a feature the field 'guid_pol' is set
> to 'some_random_uuid' as expected. I can commit the changes without a
> problem, however if instead of committing the changes I try cancelling
> them QGIS crashes with error 0xC0000005 (Access Violation).
Unfortunately this is currently a limitation of our current editing system...
When an editing signal (like "featureAdded") is emitted, doing some extra
editing actions will corrupt the undo stack because the undo command of the
previous action is not yet finished. A possible workaround could be to use
queued signal/slot connection instead of direct connection (which is the
default), so the slot execution will be delayed, and the undo stack will get to
a consistent state.
Regards
Martin
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