[Python] How to create an buttonloop with parameter in kivy, after the GUI has generated?

I have an problem with the Kivy library. I'm currently writing the front end for a ShoppinglistApp. I have an main menu, where you can select what you want to do (add List/ Shop) from where you can get to the Shop selection.

1. In the shop selection Menu are 4 shops
2. all items (Produkt) are stored in a list
3. If you select the shop, then for each item (from this shop), a button should be created.

I tried this solution:

from kivy.app import App
from kivy.metrics import dp
from kivy.lang import Builder
from kivy.properties import StringProperty
from kivy.uix.stacklayout import StackLayout
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.uix.screenmanager import ScreenManager, Screen

# the rest
class Produkt:
def __init__(self, name, amount, market):
self.name = name
self.amount = amount
self.market = market

eklist = []
for i in range(0, 100):
nn = "Banane" + str(i)
eklist.append(Produkt(nn, 0, "Baumarkt"))

# Define Screens

class FirstWindow(Screen):
pass

class SecondWindow(Screen):
pass

class ThirdWindow(Screen):
pass

class WindowManager(ScreenManager):
pass

"""Anfang der Chose"""

class Box(BoxLayout):
pass

# Gvar is a class I created for the purpose of transporting variable(s). Especially the selected shop.

class Gvar:
def __init__(self, var1):
self.var1 = var1

def get(self):
return self.var1

gvar = Gvar("default")

# SetBox ist the Class for changing the variable through the shop selection menu.
class SetBox(BoxLayout):

def set(self, market):
gvar.var1 = market
print("Set")
print(gvar.var1)


class BLE(BoxLayout):
pass

# This is the Menus which makes Problems.
class SLE(StackLayout):

def __init__(self, **kwargs):
super().__init__(**kwargs)

for p in eklist:
# In theory, this if request should always be triggered. In reality, I made the else Request to debug.
# for Text normally would appear p.name, but I changed it for debugging. Text shown(gvar.var1) is "default".
if p.market == str(gvar.get()):
b = Button(text=str(gvar.get()), size_hint=(None, None), color="blue", size=(dp(200), dp(100)),
on_press=lambda *args: self.test1(*args, str(p.name)))
b.prod = p
self.add_widget(b)

else:
b = Button(text=str(gvar.get()), size_hint=(None, None), color="green", size=(dp(200), dp(100)),
on_press=lambda *args: self.test1(*args, str(p.name)))
b.prod = p
self.add_widget(b)
market = None

# test 1 is a placeholder for a backend function
# Here I print the Produkt and gvar.var1, to debug. Here it get for gvar.var1 the in the GUI selected Value.
def test1(self, b, i):
print("Initialize test2, please wait...")
print(b.prod.name, b.prod.amount, b.prod.market, gvar.var1)

"""Ende der Chose"""

kv = Builder.load_file('einkaufsliste.kv')

class EinkaufsApp(App):
def build(self):
return kv

if __name__ == '__main__':
EinkaufsApp().run()
</code></pre> +


Here is the Kivy file:

WindowManager:
FirstWindow:
SecondWindow:
ThirdWindow:


&ltFirstWindow&gt:
name: "first"

Box:
orientation: "vertical"
size :root.width, root.height

Label:
text: "Hauptmenü"
size_hint: 1, .2
font_size: 32

Button:
text: "Einkaufen"
font_size: 32
background_normal: ' '
background_color: "#666e00"
on_release:
app.root.current = "third"
root.manager.transition.direction = "left"

Button:
text: "Einkaufsliste updaten"
font_size: 32
background_normal: ' '
background_color: "#660000"
on_release:
app.root.current = "second"
root.manager.transition.direction = "left"

&ltSecondWindow&gt:
name: "second"

BLE:
id: BLE
orientation: "vertical"
Button:
text: "to first"
size_hint: 1, .1
font_size: 24
on_release:
app.root.current = "first"
root.manager.transition.direction = "right"
TextInput:
multiline: False
size_hint: 1, .1
SVE:

&ltThirdWindow&gt:
name: "third"

SetBox:
orientation: "vertical"
size :root.width, root.height
id:SetBox

Box:
orientation: "horizontal"
size_hint: 1, .4
Button:
text: "to first"
size_hint: .2, 1
font_size: 24
on_release:
app.root.current = "first"
root.manager.transition.direction = "right"

Label:
text: "Markt auswählen"
size_hint: .8, 1
font_size: 32

Button:
text: "Supermarkt"
font_size: 32
background_normal: ' '
background_color: "#a1b2e3"
on_release:
app.root.current = "second"
root.manager.transition.direction = "left"
on_press: SetBox.set("Supermarkt")

Button:
text: "Drogerie"
font_size: 32
background_normal: ' '
background_color: "#c7bbc9"
on_release:
app.root.current = "second"
root.manager.transition.direction = "left"
on_press: SetBox.set("Drogerie")

Button:
text: "Baumarkt"
font_size: 32
background_normal: ' '
background_color: "#b4eeb4"
on_release:
app.root.current = "second"
root.manager.transition.direction = "left"
on_press: SetBox.set("Baumarkt")

Button:
text: "Elektrogerätefachhandel"
font_size: 32
background_normal: ' '
background_color: "#f4c2c2"
on_release:
app.root.current = "second"
root.manager.transition.direction = "left"
on_press: SetBox.set("Elektrogerätefachhandel")

&ltSVE@ScrollView&gt:
SLE:
id: Scrollwin
size_hint: 1, None
height: self.minimum_height

&ltSLE&gt:
# orientation: "rl-bt"
# spacing: "1dp", "1dp"


I think the problem is that kivy creates the whole GUI before I can change the variable.

Is there a way to reload the screen or do I have to make for each market/shop another screen?

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