In Kivy.kv file how do I reference a method in another class-CodePudding

I'm having difficulties understanding the relationship between kivy.kv files and class. I've coded a simple app with two classes, Test3App & Restore, with two Buttons and a Label. On clicking the Restore button I get error: AttributeError: 'Test3App' object has no attribute 'Restore'. My question is: How do I reference the Restore class in the kv or python files?

test3.py

from kivy.app import App

class Test3App(App): 

    def enlarge_text(self):
        if self.root.ids.label.font_size <90:
            self.root.ids.label.font_size  = 16
        else:
            self.root.ids.but1.text = ' font_size at\n[b][size=20]Maximum'
            self.root.ids.but1.color = 'yellow'

class Restore():

    def font_size_reset(self):
        self.root.ids.label.font_size = 16
        self.root.ids.but1.text = 'font_size\nEnlarge'
        self.root.ids.but1.color = 'white'

if __name__ == '__main__':
    Test3App().run()

test3.kv

BoxLayout:

    Button:
        id: but1
        text: 'font_size\nEnlarge'
        on_press: app.enlarge_text()
        markup: True
  
    Button:
        text: 'font_size\nRestore'
        on_press: app.Restore.font_size_reset() 
  
    Label:
        id: label
        font_size: 16
        text: str(int(label.font_size))

CodePudding user response：

Typically, you would have an instance of Restore somewhere in your app, and you would reference that instance in your kv. Here is one way to access the font_size_reset() method in your kv:

#: import Restore test3.Restore
BoxLayout:

    Button:
        id: but1
        text: 'font_size\nEnlarge'
        on_press: app.enlarge_text()
        markup: True

    Button:
        text: 'font_size\nRestore'
        on_press: Restore.font_size_reset('Abba')

    Label:
        id: label
        font_size: 16
        text: str(int(label.font_size))

The import makes the Restore class available in the kv. The call to font_size_reset() provides a meaningless argument since that method requires a self (but doesn't use it). For this to work, the font_size_reset() method must be redefined to access the root widget of the app:

class Restore():

    def font_size_reset(self):
        root = App.get_running_app().root  # get a reference to the app root widget
        root.ids.label.font_size = 16
        root.ids.but1.text = 'font_size\nEnlarge'
        root.ids.but1.color = 'white'

A slightly better approach would be to make the font_size_reset() method static, so that the meaningless argument is not needed. In this approach, the Restore class can be:

class Restore():
    @staticmethod
    def font_size_reset():
        root = App.get_running_app().root  # get a reference to the app root widget
        root.ids.label.font_size = 16
        root.ids.but1.text = 'font_size\nEnlarge'
        root.ids.but1.color = 'white'

and the corresponding test3.kv:

#: import Restore test3.Restore
BoxLayout:

    Button:
        id: but1
        text: 'font_size\nEnlarge'
        on_press: app.enlarge_text()
        markup: True

    Button:
        text: 'font_size\nRestore'
        on_press: Restore.font_size_reset()

    Label:
        id: label
        font_size: 16
        text: str(int(label.font_size))