在 kivy 中的类（屏幕）之间传递值

Question

I know that generally similar questions have been answered before. I have read them all of them. I have tried them all. Nothing seems to work for my particular case.

I am working in kivy with python 3. Not sure if that is the reason (maybe prior answers work only on python 2?).

I simply want to pass the text input from screen1_textinput (screen1_textinput.text) and the text input from screen1_textinput2 (screen1_textinput2.text), [the last one being the input from the slider of screen 1] into the text input of screen2_textinput (screen2_textinput.text).

Full code below for a simplified version of my app

## IMPORT THE DIFFERENT PACKAGES AND PROGRAMS NEEDED FOR THE APP TO WORK
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen, NoTransition, SwapTransition, FadeTransition, WipeTransition, FallOutTransition, RiseInTransition
from kivy.uix.relativelayout import RelativeLayout
from kivy.uix.label import Label
from kivy.uix.button import Button


## THE BUILDER HAS THE CODE THAT DEFINES THE APPEARANCE OF THE APP. IT IS THE KIVY CODE
Builder.load_string("""                    
############################################################SCREEN 1########################################                 
<Screen1>:

    RelativeLayout:    # RelativeLayout allows the elements of a screen to be positioned relatively to the position of the screen



        Label:    # Label is just text
            id: screen1_label    # Identifier
            text: 'This screen just shows a TextInput and a slider'    # Text that appears in the label
            pos_hint: {'x': 0.5, 'y': 0.9}    # Position of the Label in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.15, 0.05)    # Size of the Label
            font_size: (screen1_label.width + screen1_label.height) / 6     # Size of the font relative to the size of the Label
            bold: True    # Bold face




        TextInput:    # TextInput allows the user to enter text into a box
            id: screen1_textinput    # Identifier
            text: ''    # The initial text in the text box, nothing in this case
            hint_text: 'This is a TextInput. Just enter some text'    # The hint text guides the user to what input is expected
            background_color: (1, 0, 0, 1)    # The background of the TextInput
            foreground_color: (1, 1, 1, 1)    # The color of the text
            pos_hint: {'x': 0.05, 'y': 0.8}    # Position of the InputText in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.5, 0.05)    # Size of the InputText in relation to the screen
            font_size: (screen1_textinput.width + screen1_textinput.height) / 32    # Size of the font relative to the size of the TextInput
            on_text: root.manager.get_screen('screen2').screen2_textinput.text = screen1_textinput.text



        Slider:
            id: screen1_slider    # Identifier
            min: 0    # Minimum value allowed for the slider
            max: 100    # Maximum value allowed for the slider
            value: 50    # Initial value
            step: 1    # Step size
            orientation: 'vertical'    # Orientation of the slider
            pos_hint: {'x': 0.3, 'y': 0.20}    # Location of the slider in the screen (relative to the screen size)
            size_hint: (0.05, 0.25)    # Size of the slider relative to the size of the screen



        TextInput:    # TextInput allows the user to enter text into a box
            id: screen1_textinput2    # Identifier
            text: str(int(screen1_slider.value))   # The initial text in the text box, the value of the slider in this case
            background_color: (1, 0, 0, 1)    # The background of the TextInput
            foreground_color: (1, 1, 1, 1)    # The color of the text
            pos_hint: {'x': 0.5, 'y': 0.4}    # Position of the InputText in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.1, 0.05)    # Size of the InputText in relation to the screen
            font_size: (screen1_textinput2.width + screen1_textinput2.height) / 10    # Size of the font relative to the size of the TextInput





        Button:
            id: screen1_buttontoscreen2    # Identifier
            text: 'Move to screen 2'    # Text in the button
            pos_hint: {'x': 0.18, 'y': 0.02}    # Position of the Button in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.2, 0.05)    # Size of the Button in relation to the screen
            background_color: (1, 1, 1, 1)    # The background of the button
            color: (0, 0, 1, 1)    # The color of the text of the Button
            font_size: (screen1_buttontoscreen2.width + screen1_buttontoscreen2.height) / 12    # Size of the font relative to the size of the Button
            on_release:
                root.manager.current = 'screen2'    # Switch to screen 2 on release of the Button







############################################################SCREEN 2########################################
<Screen2>:

    screen2_textinput: screen2_textinput

    RelativeLayout:    # RelativeLayout allows the elements of a screen to be positioned relatively to the position of the screen


        Label:    # Label is just text
            id: screen2_label    # Identifier
            text: 'This screen just collects the inputs from Screen 1'    # Text that appears in the label
            pos_hint: {'x': 0.5, 'y': 0.9}    # Position of the Label in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.15, 0.05)    # Size of the Label
            font_size: (screen2_label.width + screen2_label.height) / 6     # Size of the font relative to the size of the Label
            bold: True    # Bold face





        TextInput:    # TextInput allows the user to enter text into a box
            id: screen2_textinput    # Identifier
            text: ''
            background_color: (1, 0, 0, 1)    # The background of the TextInput
            foreground_color: (1, 1, 1, 1)    # The color of the text
            pos_hint: {'x': 0.5, 'y': 0.45}    # Position of the InputText in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.3, 0.05)    # Size of the InputText in relation to the screen
            font_size: (screen2_textinput.width + screen2_textinput.height) / 10    # Size of the font relative to the size of the TextInput



        Button:
            id: screen2_buttontoscreen1    # Identifier
            text: 'Move to screen 1'    # Text in the button
            pos_hint: {'x': 0.18, 'y': 0.02}    # Position of the Button in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.2, 0.05)    # Size of the Button in relation to the screen
            background_color: (1, 1, 1, 1)    # The background of the button
            color: (0, 0, 1, 1)    # The color of the text of the Button
            font_size: (screen2_buttontoscreen1.width + screen2_buttontoscreen1.height) / 12    # Size of the font relative to the size of the Button
            on_release:
                root.manager.current = 'screen1'    # Switch to screen 1 on release of the Button

            """)




## THIS PART IS THE PYTHON CODE
class Screen1(Screen):
    pass




class Screen2(Screen):
    def passvariables(self):
        self.screen2_textinput.text = self.ids.screen1_textinput.text
    pass








class whAppever(App):
    def build(self):
        sm = ScreenManager(transition = FallOutTransition())
        sm.add_widget(Screen1(name = 'screen1'))
        sm.add_widget(Screen2(name = 'screen2'))
        return sm



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

My question in particular is how to pass values from the kivy language to the python language and from the python language to the kivy language and have the values updated at all times. After reviewing and trying all the prior answers, I figured out that a good way to pass values is to use this in screen 2:

class Screen2(Screen):
    def passvariables(self):
        self.screen2_textinput.text = self.ids.screen1_textinput.text
    pass

My idea was that with this code I am making the value screen2_textinput.text equal the value screen1_textinput.text

This code runs and the app is uploaded without error. However, nothing happens when I update the text of screen1_textinput.text (no update in the text of screen2_textinput). According to a prior answer to a similar question, this should work, but it does not.

The only potential workaround that I found is to use in the kivy language screen1_textinput

on_text: root.manager.get_screen('screen2').screen2_textinput.text = screen1_textinput.text

which simply passes the text inputed at screen1_textinput to screen2_textinput, but this is not what I want. I want to have the text value of screen1_textinput (screen1_textinput.text) passed to python code so that I can manipulate it, have the text value of screen1_textinput2 (screen1_textinput2.text) passed to python code so that I can manipulate in python code, put them together (much easier to manipulate strings in python than in kivy language) and then pass the resulting string back to screen2_textinput (screen2_textinput.text). And have all values updated.

I thought that this should be straigthforward, but there are tens of pages on this and nothing seems to work and update the values as I want.

Any help appreciated. I have already read and tried previous answers to similar questions. Nothing does what I am trying to do.

Thank you

Answer 1

Problem & Explanation

Your app encountered problem because self is referring to Screen2 and ids.screen1 does not exist in self.ids . If you add a print(self.ids) before the code, it will display all the ids defined in kv file under Screen2.

Snippets

 self.screen2_textinput.text = self.ids.screen1_textinput.text

Soltuion

Please refer to the example for details.

kv file

1. Add a new class ScreenManagement
2. Add screens 1 and 2 under ScreenManagement
3. Add ids for screens 1 and 2
4. Remove on_text event for screen1_textinput

Python file

1. Replace passvariables(self) with on_enter(self, *args)
2. Replace self.ids.screen1_textinput.text with self.manager.ids.screen1.ids.screen1_textinput.text
3. Add class ScreenManagement
4. Replace return sm with return ScreenManagement()
5. Remove all references to sm

Example

main.py

## IMPORT THE DIFFERENT PACKAGES AND PROGRAMS NEEDED FOR THE APP TO WORK
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen, NoTransition, SwapTransition, FadeTransition, WipeTransition, FallOutTransition, RiseInTransition
from kivy.uix.relativelayout import RelativeLayout
from kivy.uix.label import Label
from kivy.uix.button import Button


## THE BUILDER HAS THE CODE THAT DEFINES THE APPEARANCE OF THE APP. IT IS THE KIVY CODE
Builder.load_string("""
#:import FallOutTransition kivy.uix.screenmanager.FallOutTransition

<ScreenManagement>:
    transition: FallOutTransition()
    Screen1:
        id: screen1
        name: 'screen1'
    Screen2:
        id: screen2
        name: 'screen2'
                
############################################################SCREEN 1########################################                 
<Screen1>:

    RelativeLayout:    # RelativeLayout allows the elements of a screen to be positioned relatively to the position of the screen

        Label:    # Label is just text
            id: screen1_label    # Identifier
            text: 'This screen just shows a TextInput and a slider'    # Text that appears in the label
            pos_hint: {'x': 0.5, 'y': 0.9}    # Position of the Label in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.15, 0.05)    # Size of the Label
            font_size: (screen1_label.width + screen1_label.height) / 6     # Size of the font relative to the size of the Label
            bold: True    # Bold face

        TextInput:    # TextInput allows the user to enter text into a box
            id: screen1_textinput    # Identifier
            text: ''    # The initial text in the text box, nothing in this case
            hint_text: 'This is a TextInput. Just enter some text'    # The hint text guides the user to what input is expected
            background_color: (1, 0, 0, 1)    # The background of the TextInput
            foreground_color: (1, 1, 1, 1)    # The color of the text
            pos_hint: {'x': 0.05, 'y': 0.8}    # Position of the InputText in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.5, 0.05)    # Size of the InputText in relation to the screen
            font_size: (screen1_textinput.width + screen1_textinput.height) / 32    # Size of the font relative to the size of the TextInput

        Slider:
            id: screen1_slider    # Identifier
            min: 0    # Minimum value allowed for the slider
            max: 100    # Maximum value allowed for the slider
            value: 50    # Initial value
            step: 1    # Step size
            orientation: 'vertical'    # Orientation of the slider
            pos_hint: {'x': 0.3, 'y': 0.20}    # Location of the slider in the screen (relative to the screen size)
            size_hint: (0.05, 0.25)    # Size of the slider relative to the size of the screen

        TextInput:    # TextInput allows the user to enter text into a box
            id: screen1_textinput2    # Identifier
            text: str(int(screen1_slider.value))   # The initial text in the text box, the value of the slider in this case
            background_color: (1, 0, 0, 1)    # The background of the TextInput
            foreground_color: (1, 1, 1, 1)    # The color of the text
            pos_hint: {'x': 0.5, 'y': 0.4}    # Position of the InputText in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.1, 0.05)    # Size of the InputText in relation to the screen
            font_size: (screen1_textinput2.width + screen1_textinput2.height) / 10    # Size of the font relative to the size of the TextInput

        Button:
            id: screen1_buttontoscreen2    # Identifier
            text: 'Move to screen 2'    # Text in the button
            pos_hint: {'x': 0.18, 'y': 0.02}    # Position of the Button in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.2, 0.05)    # Size of the Button in relation to the screen
            background_color: (1, 1, 1, 1)    # The background of the button
            color: (0, 0, 1, 1)    # The color of the text of the Button
            font_size: (screen1_buttontoscreen2.width + screen1_buttontoscreen2.height) / 12    # Size of the font relative to the size of the Button
            on_release:
                root.manager.current = 'screen2'    # Switch to screen 2 on release of the Button


############################################################SCREEN 2########################################
<Screen2>:

    screen2_textinput: screen2_textinput

    RelativeLayout:    # RelativeLayout allows the elements of a screen to be positioned relatively to the position of the screen

        Label:    # Label is just text
            id: screen2_label    # Identifier
            text: 'This screen just collects the inputs from Screen 1'    # Text that appears in the label
            pos_hint: {'x': 0.5, 'y': 0.9}    # Position of the Label in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.15, 0.05)    # Size of the Label
            font_size: (screen2_label.width + screen2_label.height) / 6     # Size of the font relative to the size of the Label
            bold: True    # Bold face

        TextInput:    # TextInput allows the user to enter text into a box
            id: screen2_textinput    # Identifier
            text: ''
            background_color: (1, 0, 0, 1)    # The background of the TextInput
            foreground_color: (1, 1, 1, 1)    # The color of the text
            pos_hint: {'x': 0.5, 'y': 0.45}    # Position of the InputText in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.3, 0.05)    # Size of the InputText in relation to the screen
            font_size: (screen2_textinput.width + screen2_textinput.height) / 10    # Size of the font relative to the size of the TextInput

        Button:
            id: screen2_buttontoscreen1    # Identifier
            text: 'Move to screen 1'    # Text in the button
            pos_hint: {'x': 0.18, 'y': 0.02}    # Position of the Button in relation to the screen (coordinates (0,0) are lower left)
            size_hint: (0.2, 0.05)    # Size of the Button in relation to the screen
            background_color: (1, 1, 1, 1)    # The background of the button
            color: (0, 0, 1, 1)    # The color of the text of the Button
            font_size: (screen2_buttontoscreen1.width + screen2_buttontoscreen1.height) / 12    # Size of the font relative to the size of the Button
            on_release:
                root.manager.current = 'screen1'    # Switch to screen 1 on release of the Button

            """)


## THIS PART IS THE PYTHON CODE
class Screen1(Screen):
    pass


class Screen2(Screen):
    def on_enter(self, *args):
        self.screen2_textinput.text = self.manager.ids.screen1.ids.screen1_textinput.text


class ScreenManagement(ScreenManager):
    pass


class whAppever(App):
    def build(self):
        return ScreenManagement()


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

Output