[QGIS-Developer] Enable variables in QgsPropertyOverrideButton with python

[Simon Gröchenig]

Thank you for your help!

I try to implement a data defined button to select a feature subset for 
the DataPlotly plugin. You can see my code here:

https://github.com/SGroe/DataPlotly/blob/master/DataPlotly/gui/layout_item_gui.py

Unfortunately, when I click on the data defined button, it freezes a 
minute until QGIS crashes with the following error:

QList::QList qlist.h:809
QgsExpressionContext::variableNames qgsexpressioncontext.cpp:408
QgsPropertyOverrideButton::aboutToShowMenu qgspropertyoverridebutton.cpp:475
QMetaObject::activate :
QMenu::popup :
QMenu::exec :
QToolButton::paintEvent :
QToolButton::showMenu :
QToolButton::~QToolButton :

...

Do you have an idea why this happens?

Simon


Am 18.10.2019 um 01:07 schrieb Nyall Dawson:
> On Fri, 18 Oct 2019 at 06:29, Simon Gröchenig
> <simon.groechenig at salzburgresearch.at> wrote:
>> Hi,
>>
>> I want to add a QgsPropertyOverrideButton to define a expression to filter features in a python plugin. Specifically, I want to filter the features using the @altas_feature variable. However, all variables are missing in the expression dialog.
>>
>> Can anyone tell me how I can add the variables to the expression dialog?
> Hi Simon,
>
> This is all controlled via expression contexts. There's a few parts to
> the puzzle:
>
> 1. Crafting an appropriate expression context using the individual
> "scope" creation functions available through
> QgsExpressionContextUtils. You generally start with a global, project
> and layer scope, and then add additional scopes on top depending on
> the "context" in which the expression will be evaluated.
>
> So something like:
>
> context = QgsExpressionContext()
> context.appendScope( QgsExpressionContextUtils.globalScope() )
> context.appendScope( QgsExpressionContextUtils.projectScope(
> QgsProject.instance() ) )
> context.appendScope( QgsExpressionContextUtils.atlasScope( None ) )
> context.appendScope( QgsExpressionContextUtils.mapSettingsScope(
> iface.mapCanvas() ) )
>
> OR -- depending on the context -- you can get a pre-made context given
> straight to you. E.g. if the expression evaluation is occurring inside
> a layout item, then you must use
>
> context = item.createExpressionContext()
>
> instead of making your own.
>
> So this part is very dependant on the "context" in which the
> expression will be evaluated.
>
> 2. Make your dialog or widget which contains the button implement the
> QgsExpressionContextGenerator interface.
>
> 3. Register your dialog/widget as the context generator for the button
> by calling something like
>
> button.registerExpressionContextGenerator( dialog )
>
>
> Nyall
>
>
>
>
>
>
>> Regards,
>> Simon
>>
>> _______________________________________________
>> QGIS-Developer mailing list
>> QGIS-Developer at lists.osgeo.org
>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer

-- 
Simon Gröchenig MSc
MOWI - Mobile and Web-based Information Systems

Salzburg Research Forschungsgesellschaft mbH
Jakob-Haringer-Straße 5/3 | 5020 Salzburg, Austria
T: +43.662.2288-314
simon.groechenig at salzburgresearch.at
http://www.salzburgresearch.at

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20191018/01761148/attachment.html>