return a BoxLayout inside another one in Kivy? - python-3.x

Question

I'm trying to make a simple application in Python 3.5 and kivy that starts with a simple screen and when you click on it, goes to another one which shows 3 lists that let you chose the data:
The Python file:
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.listview import ListItemButton
from kivy.properties import ListProperty
from dataTopy import rlists
# Transition des ecrans:
class MainScreen(Screen):
pass
class AnotherScreen(Screen):
pass
class ScreenManagement(ScreenManager):
pass
presentation = Builder.load_file("ex44.kv")
#
class FirstListItemButton(ListItemButton):
pass
class SecondListItemButton(ListItemButton):
pass
class ThirdListItemButton(ListItemButton):
pass
class Ex44(BoxLayout):
d1 = ListProperty([str(i) for i in range(1990,2014)] )
d2 = ListProperty(['']*100)
d3 = ListProperty(['']*100)
def change(self,c):
try: self.d2,self.d3 = rlists(int(c.text))
except:
import os
CurDir = os.getcwd()
print('Can not find data in ' + CurDir)
def change1(self,c):
print('M => '+c.text)
def change2(self,c):
print('F => '+c.text)
class Ex44App(App):
def build(self):
return presentation
if __name__ == '__main__':
Ex44App().run()
The kivy file:
#: import FadeTransition kivy.uix.screenmanager.FadeTransition
#: import ListAdapter kivy.adapters.listadapter.ListAdapter
#: import ex44 ex44
ScreenManagement:
transition: FadeTransition()
MainScreen:
AnotherScreen:
<MainScreen>:
name: "main"
Button:
on_release: app.root.current = "other"
text: "Next Screen"
font_size: 50
<AnotherScreen>:
name: "other"
BoxLayout:
Ex44
Button:
color: 0,1,0,1
font_size: 25
size_hint: 0.3,0.2
text: "Back Home"
on_release: app.root.current = "main"
pos_hint: {"right":1, "top":1}
<FirstListItemButton>:
on_press: app.root.change(*args)
<SecondListItemButton>:
on_press: app.root.change1(*args)
<ThirdListItemButton>:
on_press: app.root.change2(*args)
<Ex44>:
ListView:
adapter:
ListAdapter(data=root.d1,
selection_mode='single',
cls=ex44.FirstListItemButton)
ListView:
adapter:
ListAdapter(data=root.d2,
selection_mode='single',
cls=ex44.SecondListItemButton)
ListView:
adapter:
ListAdapter(data=root.d3,
selection_mode='single',
cls=ex44.ThirdListItemButton)
When I try to run the app, it tells me: "Unknown class "
It is weird because the class Ex44 works alone but not when I'm trying to add it into the main application logic.
I've tried to return a widget instead of a BoxLayout for the class, to return Ex44 alone in the kivy file, etc. but I always get the same error in return.
Is it possible to return a BoxLayout inside another one in Kivy?

Answer 1

You are building the kv file too soon (before the class is defined). move the Builder.from_file call to the build method
...
def build(self):
return Builder.load_file("ex44.kv")