I am trying to control a screen manager from buttons in a separate class, but I cannot figure out what to set on the button on_press: statements.

Kivy file:

<HeaderSection>:anchor_x: 'center'anchor_y: 'top'BoxLayout:orientation: 'horizontal'size_hint: 1, .1id: headerLabel:text: 'My App'<ContentSection>:anchor_x: 'center'anchor_y: 'center'ScreenManager:size_hint: 1, .8Screen:name: 'home'Label:text: 'First screen'Screen:name: 'second'Label:text: 'Second screen'Screen:name: 'third'Label:text: 'Third screen'<FooterSection>:anchor_x: 'center'anchor_y: 'bottom'BoxLayout:orientation: 'horizontal'size_hint: 1, .1Button:text: 'first'on_press: root.ContentSection.manager.current = 'first'Button:text: 'second'on_press: root.current = 'second'Button:text: 'third'on_press: ContentSection.ScreenManager.current = 'third'

Python file:

from kivy.app import App
from kivy.lang import Builder
Builder.load_file('MyApp.kv')
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.anchorlayout import AnchorLayout
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.label import Label
from kivy.uix.image import Image# Declare sections
class HeaderSection(AnchorLayout):passclass ContentSection(AnchorLayout):def build(self):# Create the screen managersm = ScreenManager()sm.add_widget(FirstScreen(name='first'))sm.add_widget(SecondScreen(name='second'))sm.add_widget(ThirdScreen(name='third'))return smclass FooterSection(AnchorLayout):passclass MyAppApp(App):def build(self):#Create the sectionsfl = FloatLayout()hs = HeaderSection()cs = ContentSection()fs = FooterSection()fl.add_widget(hs)fl.add_widget(cs)fl.add_widget(fs)return flif __name__ == '__main__':MyAppApp().run()

I have tried various methods:

on_press: root.parent.ContentSection.ScreenManager.current = 'home'
on_press: root.parent.ContentSection.manager.current = 'home'
on_press: root.ContentSection.manager.current = 'home'

I feel like it is a scoping issue, errors say things like:

AttributeError: 'FooterSection' object has no attribute 'ContentSection'

So my app has the following hierarchy:

FloatLayoutHeaderSectionContentSectionScreenManagerFirstScreenSecondScreenThirdScreenFooterSectionButton for FirstScreenButton for SecondScreenButton for ThirdScreen

So I need to traverse up a level into FloatLayout, then drill down into ContentSection to access the screen manager.

Navigating widget trees has been a pain for me, and AFAIK you can't traverse the widget tree the way you'd like.

You can, however, simplify your widget tree, make sure everything shares the same root, and use ids.

Here's how I did it (I also moved everything to kv language):

kv

FloatLayout:AnchorLayout:anchor_x: 'center'anchor_y: 'top'Label:size_hint: 1, .1text: 'My App'AnchorLayout:anchor_x: 'center'anchor_y: 'center'ScreenManager:id: managersize_hint: 1, .8Screen:name: 'first'Label:text: 'First screen'Screen:name: 'second'Label:text: 'Second screen'Screen:name: 'third'Label:text: 'Third screen'AnchorLayout:anchor_x: 'center'anchor_y: 'bottom'BoxLayout:orientation: 'horizontal'size_hint: 1, .1Button:text: 'first'on_press: root.ids.manager.current = 'first'Button:text: 'second'on_press: root.ids.manager.current = 'second'Button:text: 'third'on_press: root.ids.manager.current = 'third'

python

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.anchorlayout import AnchorLayout
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.label import Label
from kivy.uix.image import Imageclass MyAppApp(App):def build(self):return Builder.load_file('MyApp.kv')if __name__ == '__main__':MyAppApp().run()