[Python] How do I get signals of checkboxes checked in mdlist?

Using KivyMD and Python, when the program displays the mdlist you can check the checkboxes but can't access the on_active status:

from kivy.uix.gridlayout import GridLayout
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.core.window import Window
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivymd.app import MDApp
from kivymd.uix.screen import Screen
from kivymd.uix.list import MDList, MDListItemHeadlineText,MDListItem,MDListItemLeadingIcon,\
MDListItemSupportingText,MDListItemTertiaryText,MDListItemTrailingCheckbox
from kivy.uix.scrollview import ScrollView

class Origin(Screen):

def test2(self):
print('something.......')
def full_list(self):


Creating a list to simulate a fetchall result:

listadeobjetos = [['ana','Belgium','blue'],['juan','Uruguay','yellow'],['mary','Congo','brown']]

list_view = MDList()


Trying to put an index number to each row:

numero_fila = 0

for i in listadeobjetos:
fila=MDListItem(
MDListItemHeadlineText(
text = 'NAME: ' + i[0],
),
MDListItemSupportingText(
text= 'COUNTRY ' + i[1] ,
),
MDListItemTertiaryText(
text='ONE COLOR '+ i[2] ,
),
MDListItemTrailingCheckbox(

# here are all my attempts

group= 'seleccion',
#on_active= lambda x= 'A': self.parent.ids.Results.testcheck(x),
#on_active= self.parent.ids.Origin.test2,
#on_active= self.parent.ids.Results.test3,
on_active= lambda x= 'SOMETHING': print(x),
),
)
numero_fila += 1
fila.focus_color= 1,0,1,.33
fila.id= str(numero_fila)
list_view.add_widget(fila)

self.parent.ids.Results.ids.scroll.add_widget(list_view)

self.parent.current = 'RESULTADOS'

class Results(Screen):

def testcheck(self, ins ):
print('TRYING TO GET SOMETHING .....'+ ins)

def test3(self):
print('maybehere.....')

class Window_Manager(ScreenManager):
pass




trust = Builder.load_file('the_question.kv')

class MrhApp(MDApp):

def build(self):
Window.borderless = True
return trust


app = MrhApp()
app.run()


kv file:

#:kivy 2.3.1

Window_Manager:
Origin:
id: Origin
Results:
id: Results

<Origin>
id:'Origin'
name: 'ORIGIN'
canvas.before:
Color:
rgba: 0.188, 0.188, 0.204,1
Rectangle:
pos: self.pos
size: self.size
GridLayout:
cols: 1
rows: 2
row_force_default: True
row_default_height: 50
padding: 10
spacing:40

GridLayout:
cols: 3
rows: 1
size_hint_y: .08
padding: 10

Label:
size_hint_y: None
size_hint_x: None
width: 50
height: 50
pos_hint: {'center_x':0.2}
text: 'PLEASE'

Label:
id:banner_centro
text:'WILL BE A QUESTION'
halign: 'center'
color: 1,0,0,1
font_size: 20

Button:
size_hint_y: None
size_hint_x: None
width: 50
height: 50
pos_hint: {'center_x':0.8}
on_release: app.stop()
background_color: 0.188, 0.188, 0.204,1
background_normal: ""
text: 'LOGOUT'

GridLayout:
cols: 2
spacing: 50,20
padding: 10,10



Label:
text: 'CLICK ON BUTTON TO GET FULL LIST'

Button:
size_hint: None,None
height: 150
width: 135
id: fulllist
on_release: app.root.current= root.full_list()
background_color: 0.188, 0.188, 0.204,1
background_normal: ""
text: 'FULL LIST'



<Results>
name: 'RESULTADOS'

GridLayout:
cols: 1
rows: 3
padding: 10
spacing:20
canvas.before:
Color:
rgba: 0.188, 0.188, 0.204,1
Rectangle:
pos: self.pos
size: self.size
GridLayout:
cols: 3
rows: 1
size_hint_y: .08
padding: 10

Label:
size_hint_y: None
size_hint_x: None
width: 50
height: 50
pos_hint: {'center_x':0.2}
text: ' here was an image'

Label:
id:banner_centro
text:'this is the question'
halign: 'center'
font_size: 20
color: 1,0,0,1

Button:
size_hint_y: None
size_hint_x: None
width: 50
height: 50
pos_hint: {'center_x':0.8}
on_release: app.stop()
background_color: 0.188, 0.188, 0.204,1
background_normal: ""
text: 'LOGOUT'



ScrollView:

id:scroll
size_hint_y: .8
padding: 5



GridLayout:
cols: 1
rows: 1
spacing: 50,50
padding:10
size_hint_y: .08

Button:
id: button_back
background_color: 0.188, 0.188, 0.204,1
text:'BACK'
size_x: 40
color: 0.773, 0.525, 0.714,1
on_release: app.root.current= 'ORIGIN'

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