Hello Raspberry Pi people,

I am using Kivy v1.11.1 on my Raspberry Pi with Python v3.7.3. The goal is to use a GPIO input to toggle the button state (parallel use of a real button and the touchscreen button possible). To change the state of the button I used the StringProperty that I attached to the state property in the KV file.

As you can see, the variable Gui.key_state will change (this is why I added the loop function every second). And also the initial value of RoundedButton text property is set to "normal" (I chose to attach my key_state StringProperty also to the text property so I can see if it is working).

The issue is, that the property does not get updated in the gui as it should (if I understand the kivy docs correctly).

Best regards and thanks for the help, Martin


# -*- coding: utf-8 -*-

import kivy
from kivy.app import App
from kivy.properties import StringProperty
from kivy.properties import ObjectProperty
from kivy.uix.widget import Widget
from kivy.clock import Clock

import RPi.GPIO as GPIO

class Gui(Widget):

    input_key = 12 #number of pin
    key_state = StringProperty('normal')

    def __init__(self, **kwargs):
        Clock.schedule_interval(self.loop, 1)
        super(Gui, self).__init__(**kwargs)

    def gpio_isr(obj):     
        if GPIO.input(Gui.input_key) == 0: #key pressed
            Gui.key_state = 'down'
            Gui.key_state = 'normal'       

    GPIO.setup(input_key, GPIO.IN, pull_up_down=GPIO.PUD_UP)
    GPIO.add_event_detect(input_key, GPIO.BOTH, callback=gpio_isr, bouncetime=200)

    def loop(self, *args):

class GuiApp(App):

    def build(self):
        return Gui()

if __name__ == '__main__':


#:kivy 1.11.1

    background_color: (.0, .0, .0, .0) # delete background property
            rgba: (.5, .5, .5, 1) if self.state=='normal' else (.0, .569, .863, 1)  # visual feedback of press
            pos: self.pos
            size: self.size
            radius: [5,]

        pos: self.parent.pos
        size: self.parent.size
        size_hint: None, None
        state: root.key_state
        text: root.key_state

  • Abandoned post by Unregistered user.
    – Milliways
    May 7, 2023 at 23:12

1 Answer 1


Ok. One thing that works is using the isr add_event_detect to call the GUI function that is shared with the key. Then a synchronize routine every 100 ms will set the states of the buttons (in this context I can use the ids function). Yeah, it's bad. But do you have any better idea?

class Gui(Widget):
    key_state = False

    def gpio_isr(obj):
        Gui.key(Gui, False) if GPIO.input(Gui.input_key) else Gui.key(Gui, True) # inverted buttons

        GPIO.setup(12, GPIO.IN, pull_up_down=GPIO.PUD_UP) # example pin 12
        GPIO.add_event_detect(12, GPIO.BOTH, callback=lambda x: Gui.gpio_isr(), bouncetime=20) # routine can not be found if lambda is not used.

    def __init__(self):
        Clock.schedule_interval(self.loop, .1) # set a synchronize-routine every 100 ms.
        super(Gui, self).__init__()

    def loop(self, *args):        
        self.ids.key.state = 'down' if self.key_state else 'normal'

    def key(self, *args):
        self.key_state = args[0] # because when I try to change the state here it returns AttributeError: 'kivy.properties.DictProperty' object has no attribute 'key'

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