[QGIS-Developer] QgsRenderCategory with or without uuid?

[Raymond Nijssen]

Hi developers,

We recently bumped into an issue which took quite some to solve The 
QgsRenderCategory objects we created in python resulted in a layer with 
incorrectly working "layer legend". When unchecking and checking the 
categories in that layer legend, it's always the first category being 
turned off/on. It appears to be related to the uuid. Here's the code for 
the fix:

https://gitlab.com/terglobo/qgis_dso_plugin/-/commit/f2e492e69f19f426bbe43355d18821ce4807ab5c

After clicking around a bit, opening the layer style panel too, 
something gets updated and everything starts working correctly. Saving 
the style to .qml also seems to trigger an update.

My question is, should the old way of creating an empty 
QgsRenderCategory and setting the value, label and symbol later, not be 
used anymore? In that case, the python cookbook needs to be updated.

Or is this a bug that needs to be fixed?

Since QGIS can somehow fix this internaly, it would be nice if the 
QgsRenderCategory constructor would simply create and set a uuid 
automatically, or otherwise get an updateUuid() method. Instead of 
importing uuid and putting uuid=str(uuid.uuid4()) in your python code.

Regards,
Raymond (and Richard)


api docs:
https://qgis.org/pyqgis/master/core/QgsRendererCategory.html

cookbook:
https://docs.qgis.org/testing/en/docs/pyqgis_developer_cookbook/vector.html#categorized-symbol-renderer