Create a drop-down menu in a QGIS Processing script?

Question

I'm trying to write a QGIS processing script using the new API (3.4), but I hardly find any documentation. Based on this excellent resource by Anita Graser (https://anitagraser.com/2018/03/25/processing-script-template-for-qgis3/), I could manage to set up a basic script that mostly fits my needs.

But I have some fixed-value (eg: ['walking', 'car']) options for which I'd like to include drop-down menus. I assume that I have to use a QgsProcessingParameterString but using the available documentation, I could'nt figure out how to do it.

Answer 1

The PyQGIS documentation can be searched for all potential QgsProcessingParameter classes: https://qgis.org/pyqgis/master/search.html?q=QgsProcessingParameter&check_keywords=yes

For your use case, QgsProcessingParameterEnum seems fitting.

Here's a usage example from qgis-latlontools-plugin:

self.addParameter(
 QgsProcessingParameterEnum(
 self.PrmCoordinateOrder,
 tr('Coordinate order when using 1 field'),
 options=[tr('Lat,Lon (Y,X) - Google map order'),tr('Lon,Lat (X,Y) order')],
 defaultValue=0,
 optional=True)
 )

• Souvik Sankar Mitra: 'QgsProcessingParameterEnum' gives value as Integer i.e. the index. Can you tell me how to access the value from it in processing script
• LeasMaps: Open the plugin in Github, find PrmCoordinateOrder and do a check for where it is used (click on it, select references). There is also an example with more than 2 options further down