Getting QGIS Project data from outside Python script

Question

In my project, I have to connect .Net with the QGIS app, so I need to know how an outside script can get data from QGIS.

I can run this script from .Net perfectly:

from qgis.PyQt.QtWidgets import QMessageBox
from qgis.core import *
from qgis.gui import *
from qgis.utils import *
import sys
import os
def main ():
 # Create a reference to the QgsApplication.
 # Setting the second argument to True enables the GUI. We need
 # this since this is a custom application.
 strRuta = r"C:\Program Files\QGIS 3.22.11\apps\qgis-ltr"
 os.environ['QGIS_PREFIX_PATH'] = strRuta
 # load providers
 qgs = QgsApplication([], True)
 # Supply the path to the qgis install location
 qgs.setPrefixPath(strRuta, True)
 qgs.initQgis()
 # QgsApplication.setPrefixPath(r"C:\Program Files\QGIS 3.22.11\apps\qgis-ltr", True)
 QMessageBox.warning(None, "AVISO", QgsApplication.showSettings())
 project = QgsProject.instance()
 listLayers = QgsProject.instance().mapLayersByName('MONTE')
 QMessageBox.information(None, "Aviso monte:", str(len(listLayers)))
 # Write your code here to load some layers, use processing
 # algorithms, etc.
 # Finally, exitQgis() is called to remove the
 # provider and layer registries from memory
 qgs.exitQgis()
if __name__ == "__main__":
 main()

However, in this line QMessageBox.information(None, "Aviso monte:", str(len(listLayers))), I obtain 0, but I have charged a MONTE layer in qgis manually without code

I am using QGIS 3.22.11.

• Taras: Please, do not forget about "What should I do when someone answers my question?"

Answer 1

You have to load a project. QgsProject.instance() returns the empty project, because you didn't load any project.

Add this line: project.read("c:/path/to/project.qgz")

project = QgsProject.instance()
project.read("c:/path/to/project.qgz")
listLayers = QgsProject.instance().mapLayersByName('MONTE')
QMessageBox.information(None, "Aviso monte:", str(len(listLayers)))

• Andrés Rodríguez: Yes, but I have some layers in qgis that I have imported from postgis, and I would like to make some operations with them in this script. Is there any way to do this?
• Andrés Rodríguez: How can I access to the project and the layers that are charged in qgis from this script ?