QGIS plugin - NameError: name 'iface' is not defined while importing class from other file

Question

Here is my class

class aClassName():
    def __init__(self):
        #do something...

        iface.setActiveLayer(QgsProject.instance().mapLayersByName('someName')[0])

        #do something
    ...

The class calls a number of methods from iface such as setActiveLayer, .mapCanvas().zoomToSelected() etc in different functions. It runs properly when it is called in the same file.

But when I tried to use the class by importing it into another file:

from theClassFile import aClassName

The error message showed up and said :

NameError: name 'iface' is not defined

even if adding from qgis.utils import iface to theClassFile with reference from here.

I just began to use PyQGIS last month.

Here is my QGIS version:

Answer 1

I tried in Python console, the following code works.

The content of the file theClassFile.py :

class aClassName():  
    def __init__(self):

        # Replace the name of your layer
        iface.setActiveLayer(QgsProject.instance().mapLayersByName('alaska')[0])
        print('OK !')

The contents of the main script :

from qgis.utils import iface
from qgis.core import *

import sys 
# Path of theClassFile.py directory
sys.path.append(r'C:/Users/v.bre/Desktop/test/iface_double_scripts/')

from theClassFile import aClassName

aClassName()

I have two layers in my QGIS project. With this code, I change the active layer and I print a message. There are many bugs, if you modify theClassFile.py, QGIS will not take the changes into account. To solve this problem, sometimes think about restarting your QGIS.

Try this code and get back to me.