Hi Matthias
I remember there was a performance consideration leading to the
emitSignal parameter in changeAttributeValue. But I don't know if it is
still needed, seems to be only used from field calculator, offline
editing and a label tool.
So +1 for your proposal.
Regards,
Marco
On 06.01.2014 14:01, Matthias Kuhn wrote:
Hi,
Currently,when the field calculator does changes to attributes
(modification, not adding a new column) it blocks signals of the
vector layer while doing this. This leads e.g. to bug #9268 [1], that
the attribute table is not updating properly. The fix would be very
easy (i.e. remove the blockSignals() call) but I wanted to ask first,
if there is a reason not to do this.
The main reason why I am afraid is, that apart from the blockSignals()
call, there is also the paramter emitSignal specified as false in the
call to vectorlayer->changeAttributeValue(). This parameter is
currently not working, so I suppose that the blockSignals() call was
introduced as a workaround.
However, there was a good reason, to block the signals explained in
issue #7071 [2], fixed by Jürgen, that at the time when we only
supported one iterator per layer, emitting this signal would break the
update process and produce only partially updated results. This is
fortunately no longer the case, so this reason can be considered
obsolete.
Another reason which I could imagine (but I have no proof of) is that
for big layers, emitting the signal for each feature can possibly take
a long time. However, if this is actually the case we should rather
think about batching the signal or fix unperformant consumer slots of
this signal.
Be aware, that at the current state, there is no possibility, neither
for plugins nor in QGIS core, to get reliable push-notifications when
an attribute changes.
So my proposal is:
* Remove the blockSignal calls and let attribute changes always be
promoted
* If there are problems introduced, lets fix the problems instead of
working around them at the cost of unreliability
* Don't fix the emitSignal parameter for
QgsVectorLayer::changeAttribute and deprecate it for future removal.
If there is no objection, I would vote to make this changes before the
QGIS 2.2 freeze
Best
Matthias
[1] http://hub.qgis.org/issues/9268
[2] http://hub.qgis.org/issues/7071
_______________________________________________
Qgis-developer mailing list
Qgis-developer@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/qgis-developer
--
Dr. Marco Hugentobler
Sourcepole - Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentob...@sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee
_______________________________________________
Qgis-developer mailing list
Qgis-developer@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/qgis-developer
