Updating a label returns blank screen in Kivy (Python)

Question

I'm trying to display the data from temperature sensor in my Kivy App. I found some help material from this website but I've been trying to integrate the code with my sensor but it just returns a blank screen. What am I doing wrong?

.py file:

from kivy.app import App
from kivy.properties import ObjectProperty, StringProperty
from kivy.uix.boxlayout import BoxLayout
from kivy.clock import Clock
from kivy.uix.label import Label
from kivy.uix.widget import Widget

import time
from w1thermsensor import W1ThermSensor


sensor = W1ThermSensor()



class LabelWidget(BoxLayout):
    manager = ObjectProperty(None)
    def __init__(self, **kwargs):
        super(LabelWidget, self).__init__(**kwargs)
        Clock.schedule_interval(self.getTemp, 2)
    def getTemp(self, dt):
        temperature = sensor.get_temperature()
        thetemp = temperature 
        self.manager.ids.TempLabel.text = str(thetemp)



class labeltestApp(App):

    def build(self):
        return LabelWidget()

if __name__ == "__main__":
    labeltestApp().run()

.kv file:

LabelWidget:
    Label:
        id: TempLabel
        text: 'temperature'
        text_size: self.size
        halign: 'right'
        valign: 'middle'

Answer 1

Root Cause - Blank Screen

When your application runs, there were two root instantiated. One of the root ( LabelWidget: ) is from your kv file, labeltest.kv , and the other root is from return LabelWidget() . The root used by your app is from return LabelWidget() which does not has an associated modal view.

Solution

In your kv file, labeltest.kv ; replace root rule , LabelWidget: with class rule , <LabelWidget>:

Problem 2

In the minimal code provided, there is no use of Kivy ScreenManager. The code, self.manager.ids.TempLabel.text = str(thetemp) will cause an error.

Solution

Remove manager from self.manager.ids.TempLabel.text = str(thetemp) . The end result is self.ids.TempLabel.text = str(thetemp)