Changing the screen and running a function on kivyMD?

Question

I am learning Kivy, but I do not kown how to change a screen and running a funtion at the same time.

Where should I declare my funtion so the button have access to the code and can run the function?

from kivymd.app import MDApp
from kivy.lang.builder import Builder
from kivy.uix.screenmanager import ScreenManager, Screen

screen_helper = """
ScreenManager:
    MenuScreen:
    FunctionScreen:

<MenuScreen>:
    name: 'menu'
    MDRectangleFlatButton:
        text: 'Function'
        pos_hint: {'center_x':0.5,'center_y':0.5}
        on_press: root.manager.current = 'function screen'

<FunctionScreen>:
    name: 'function screen'
    MDRectangleFlatButton:
        text: 'Back'
        pos_hint: {'center_x':0.5,'center_y':0.1}
        on_press: root.manager.current = 'menu'

"""


class MenuScreen(Screen):
    pass


class FunctionScreen(Screen):
    pass


# Create the screen manager
sm = ScreenManager()
sm.add_widget(MenuScreen(name='menu'))
sm.add_widget(FunctionScreen(name='function'))


class DemoApp(MDApp):

    def build(self):
        screen = Builder.load_string(screen_helper)
        return screen

    # def funtion(self):
        # do stuff and then go to menu screen



DemoApp().run()

Should I try maybe, add the on_opress atribute in the build function?

Can you guys help me?

Answer 1

There are several convenient places to place the function(). One is in the MenuScreen, and in that case, it would be referenced in the kv files as:

root.function()

Another convenient place is in the DemoApp, and in that case, the reference would be:

app.function()

So, here is a version of your code tht puts the function() in the App:

from kivymd.app import MDApp
from kivy.lang.builder import Builder
from kivy.uix.screenmanager import Screen

screen_helper = """
ScreenManager:
    MenuScreen:
    FunctionScreen:

<MenuScreen>:
    name: 'menu'
    MDRectangleFlatButton:
        text: 'Function'
        pos_hint: {'center_x':0.5,'center_y':0.5}
        on_press:
            root.manager.current = 'function screen'
            app.function()

<FunctionScreen>:
    name: 'function screen'
    MDRectangleFlatButton:
        text: 'Back'
        pos_hint: {'center_x':0.5,'center_y':0.1}
        on_press: root.manager.current = 'menu'

"""


class MenuScreen(Screen):
    pass


class FunctionScreen(Screen):
    pass


class DemoApp(MDApp):

    def build(self):
        sm = Builder.load_string(screen_helper)
        return sm

    def function(self):
        # do stuff and then go to menu screen
        print('in function')


DemoApp().run()

Note that the lines of your code that built a ScreenManager have been deleted as they are unnecessary.