How can a dynamic class access another class' attributes such as root.width/root.height? - kivy

Question

Here is a class NewWindow with a GridLayout in a FloatLayout, a dynamic class NewButton inheriting from ToggleButton, and a class in the Python file that receives the GridProperty in order to add_widget NewButton into it.
The overall goal is to have a button that adds a toggle button into the grid layout, and for all button/toggle buttons to be able to dynamically change size for different screen resolutions. The issue I'm having is that I can't simply write (root.width**2 + root.height**2) / 12**4 for NewButton. I think it's because "root" in NewWindow is not the same as "root" in NewButton, but I do not have a solution.
Is there a way for me to access NewWindow's "root" inside of NewButton? I ultimately just want all my buttons to match each other's sizes and for it to be dynamic, so I don't want to simply write a static "30" for font_size.
# File: main.kv
<NewWindow>:
parentGrid: parentGrid
FloatLayout:
Button:
text: "Add New Button"
pos_hint: {"x": 0.05, "top": 0.7}
size_hint: .4, 0.05
font_size: (root.width**2 + root.height**2) / 12**4
on_release:
root.addButton()
GridLayout:
id: parentGrid
cols: 1
pos_hint: {"x": 0.5, "top": 0.7
size_hint: .4, .5
<NewButton#ToggleButton>:
text: "BUTTON"
size_hint_y: ???
#height: ???
font_size: ???
# Cannot simply use root.width or root.height, also size_hint: .4, 0.05 doesn't work
# File: MainApp.py
class NewWindow(Screen):
parentGrid = ObjectProperty(None)
def AddButton(self):
self.parentGrid.add_widget(NewButton())

Answer 1

You are right the two roots are different. One is as you say the size of the new window, but the other would only be the size of GridLayout. The problem you have with the size_hint is because you are using a GridLayout. If you can change to example a BoxLayout that would work if not the size_hint: None, None and then set the size: would work:
To get the the NewWindow Root use app.root.width and app.root.heigth
main.py:
from kivy.app import App
from kivy.lang import Builder
from kivy.properties import ObjectProperty
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.togglebutton import ToggleButton
class NewButton(ToggleButton):
pass
class NewWindow(Screen):
parentGrid = ObjectProperty(None)
def __init__(self, **kwargs):
super(NewWindow, self).__init__(**kwargs)
def addButton(self):
print('test')
self.parentGrid.add_widget(NewButton())
class Manager(ScreenManager):
pass
class TestApp(App):
def build(self):
return Builder.load_file('test.kv')
if __name__ == '__main__':
TestApp().run()
.kv:
Manager:
NewWindow:
name: 'new'
<NewButton#ToggleButton>:
text: "BUTTON18"
pos_hint: {"x": 0.05, "top": 0.7}
size_hint_x: None
size_hint: 1, 1
#size: 10, 10
font_size: (app.root.width**2 + app.root.height**2) / 12**4
<NewWindow>:
parentGrid: parentGrid
FloatLayout:
Button:
text: "Add New Button"
pos_hint: {"x": 0.05, "top": 0.7}
size_hint: .4, 0.05
font_size: (root.width**2 + root.height**2) / 12**4
on_release:
root.addButton()
BoxLayout:
id: parentGrid
cols: 1
pos_hint: {"x": 0.5, "top": 0.7}
size_hint: .4, .5
canvas:
Color:
rgba: 1,1,1,1
Rectangle:
size: self.size
pos: self.pos
# Cannot simply use root.width or root.height, also size_hint: .4, 0.05 doesn't work
I did also add the screenmanager to be able to access the width and height
Hope this helps