[GIS] Add layer to map in qgis3 via a python script

pyqgisqgis-3

I'm trying convert my old plugin to QGIS3 and one part is to create a shapefile, and afterwards load it to the Layer menu like this:

from qgis.core import QgsVectorLayer, QgsProject
layer = QgsVectorLayer('c:/dev/test.shp', 'test', "ogr")
print(layer.isValid())
QgsProject.instance().addMapLayer(layer)

The python console returns True and the Layer appears in the layer list, hence I can't add features to it when I have toggled editing:

However, if I remove the layer from layer list and add the layer with the same code in the Python console I have no problem with adding a feature.

Any suggestions for what I can try?

Best Answer

I solved the problem, I believe that the layer was loaded without fields in some way. It was wired though, it had an 'ID' column when I checked in the Attribute table, but somehow I believe that it had something todo with error anyway. When I changed the layer creation method (by the help of the code in this question) the layer was loaded correctly from the plugin.

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QGIS – Usage of QgsTask and QgsTaskManager

There's a typo in that script - it should be isCanceled() (one l, not two)

You should also add your task to the global task manager instead of creating a new manager:

QgsApplication.taskManager().addTask(task)

One thing to be very careful about is never to create widgets or alter gui in a task. This is a strict Qt guideline - gui must never be altered outside of the main thread. So your progress dialog must operate on the main thread, connecting to the progress report signals from the task which operates in the background thread.

QGIS 3 – Setting Relative Path to SVG File in Plugin Folder for .SLD Files with PyQGIS

In QGIS2.18 I could specify the path to the svg marker as: :/PLUGIN_NAME/IMAGE_FOLDER/FILENAME.svg

Paths that start with :/ (and qrc:///) are paths to Qt resources. I assume there is a .qrc file which has been compiled/packaged to a resources.py file. The file from QGIS 2 is not compatible with QGIS 3 and you need to recreate the file to be able to continue to use resources (and therefore also paths that start with :/)

Alternatively you can also specify the full path to the svg file (as you post yourself as an answer).

This can also be automated, the following snippet can be used to determine the plugin path:

import os 
plugin_path = os.path.dirname(os.path.realpath(__file__)) # Potentially fix subdirectories

Then check if this path is already configured and add it if missing

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Best Answer

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