Passing values between the screens Kivy-CodePudding

I have an Open CV Kivy app that has 2 screens. The screen 1 (ProblemWindow) will get the user input and The live video from the webcam will be shown on screen 2 (StepsWindow). However, I need to pass one of the values (Spinner id: problem_id) from screen 1 (ProblemWindow) into screen 2 (StepsWindow) and also use the value in the python file for additional logic.

Can anyone please guide me on how to achieve this? I am stuck here.

Python File:

# importing kivy dependencies
from kivy.app import App
from kivy.clock import Clock
from kivy.graphics.texture import Texture
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.lang import Builder
from kivy.uix.widget import Widget

# import other dependencies
import cv2 as cv
import numpy as np
from cv2 import aruco 

# defining different screens
class WindowManager(ScreenManager):
    pass

class ProblemWindow(Screen):
    def selected_problem(self, value):
        self.ids.click_label.text = f'selected problem: {value}'
        return value

class StepsWindow(Screen):
    def __init__(self, **kwargs):
        print('Steps Window')
        super().__init__(**kwargs)
        # Capture the frames from the webcamera
        self.capture = cv.VideoCapture(0)
        Clock.schedule_interval(self.run_webcam, 1.0/30.0)

    def run_webcam(self, *args):
        """Run continuously to get webcam feed"""
        ret, frame = self.capture.read()
        # Flip Horizontal and convert image into texture
        buf = cv.flip(frame, 0).tobytes()
        img_texture = Texture.create(size = (frame.shape[1], frame.shape[0]), colorfmt = 'bgr')
        img_texture.blit_buffer(buf, colorfmt = 'bgr', bufferfmt = 'ubyte')
        self.ids.web_cam.texture = img_texture # id is the id of the image from the kv file. 

kv = Builder.load_file('window_manager.kv')

class main(App):
    def build(self):
        return kv

if __name__ == '__main__':
    main().run()
    cv.destroyAllWindows()

Kivy File:

WindowManager:
    ProblemWindow:
    StepsWindow:

<ProblemWindow>:
    name: "problem_window"
    GridLayout:
        rows: 3
        size: root.width, root.height
        Label:
            id: click_label
            text: "Select a Problem"
            font_size: 32
            height: 20
        Spinner:
            id: problem_id
            text: "selected problem"
            values: ["Problem_1", "Problem_2"]
            on_text: root.selected_problem(problem_id.text)
            size_hint: 0.5, 0.5
        Button:
            text: "Show Steps"
            font_size: 32
            size_hint: 0.3, 0.3
            on_release: 
                app.root.current = "steps_window"
                root.manager.transition.direction = "left"

<StepsWindow>:
    name: "steps_window"
    web_cam: web_cam
    GridLayout:
        rows: 3
        size: root.width, root.height
        Label:
            id: problem_name
            text: "Selected Problem Name should come here"
            font_size: '42'
            size_hint_y: None
            height: 50
        Image:
            id: web_cam
        Button:
            text: "Exit"
            font_size: 32
            size_hint: 0.1, 0.1
            on_release: 
                app.root.current = "problem_window"
                root.manager.transition.direction = "right"

CodePudding user response：

You can let Kivy handle that for you, by assigning the text to the problem_name Label using Properties. First, assign an id to the ProblemWindow Screen:

WindowManager:
    ProblemWindow:
        id: pw
    StepsWindow:

Then use that id to assign the text:

    Label:
        id: problem_name
        text: root.manager.ids.pw.ids.problem_id.text
        font_size: '42'
        size_hint_y: None
        height: 50

Because the text is assigned based on ids and Properties, Kivy will keep it updated for you. If you tried to use root.manager.get_screen('problem_window'), it would not work because Kivy will not repeat method calls to update a value.