Kivy not Responsing

[Peanut]

Hello, I have this code where if I press the button and there is some processing happening, the app starts to crash if I do anything, like pressing the button and then starting to type numbers in the text field. How can I fix this?

```Kivy 2.3.0
Kivymd 1.1.1
request 2.32.2```

import time

from kivy.lang import Builder

import requests

from kivymd.app import MDApp

class Example(MDApp):

    def build(self):

        # Define the KV layout as a string

        self.kv = """

MDFloatLayout:

    MDCard:

        orientation: "vertical"

        size_hint: None, None

        size: "350dp", "300dp"

        pos_hint: {"center_x": 0.5, "center_y": 0.5}

        padding: 25

        spacing: 25

        radius: [20, 20, 20, 20]

        # Mobile Number Input Field

        MDTextField:

            mode: "round"

            id: mobile_number

            hint_text: "9xxxxxxxxx"

            helper_text: "Must be 10-digit only"

            helper_text_mode: "on_focus"

            icon_right: "cellphone"

            input_type: "number"

            max_text_length: 10

            size_hint_x: 1

        # Login Button

        MDFillRoundFlatButton:

            text: "Login"

            size_hint_x: 0.5

            pos_hint: {"center_x": 0.5}

            on_release: app.send_mobile_number()

        """

        return Builder.load_string(self.kv)

    def send_mobile_number(self):

        mobile_number = self.root.ids.mobile_number.text

        api_url = "api_here"

        time.sleep(5)

        payload = {"mobile_number": mobile_number}

        # Send POST request

        try:

            # response = requests.post(api_url, json=payload)

            # print(response.json())

            print("Mobile Number:", mobile_number)

        except requests.exceptions.RequestException as e:

            print("Error:", e)

    def on_leave(self):

        self.root.ids.mobile_number.text = ""

# Run the app

Example().run()

[Peanut]

I added this video for more clarity.

[ElliotG]

The problem is the call to time.sleep().  Kivy is an event based system.  The events are handled in the main event loop.  The main loop is started when you call run.  Your functions generally return to the event loop.  When you use sleep on the main thread, you are stalling the event loop - so things lock up.

There is a description of the event loop (or main loop) is here: https://kivy.org/doc/stable/guide/events.html

I also recommend you use kivy's URL request rather than requests.  It is non blocking and uses callbacks.  See: https://kivy.org/doc/stable/api-kivy.network.urlrequest.html#module-kivy.network.urlrequest

If you want to create a delay you need to schedule the next event on the event loop.  Use Clock.schedule_once, see: https://kivy.org/doc/stable/api-kivy.clock.html#module-kivy.clock

I hope this helps.  Understanding the main loop is critical to understanding how kivy works.

[Peanut]

Hello ElliotG, the Kivy URLRequest works perfectly. I have been reading about events, properties in Kivy, and also the Kivy Clock. Do you have any examples in terms of code? I’ll be using this in a scenario where I need to wait for a response from hardware.  Let’s say I need to wait for a response from hardware, which takes around 5 seconds for processing and response.

[ELLIOT GARBUS]

Please explain more about the api to check the hw.   Is it non-blocking?  Can you check if the hardware is ready?  If so you could schedule use schedule_interaval to poll the hardware and see if it is ready.

If reading the hw is blocking and you want to schedule reading the hw after you know it will be ready, use schedule_once.

Think about it like this the schedule_once method of Clock is putting a function on a list.  Inside the kivy run loop, kivy is checking the schedule to see it if is time to run the call back.  When the time is up, the callback is executed.

If you'd like to see an example, provide more details on the hw, and I'll share a short example.

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Subject: [kivy-users] Re: Kivy not Responsing

 

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[Peanut]

  Here is an example of code that needs to wait before I can get a response. This happens while scanning. The problem is that if I click something while a paper is being scanned, the app freezes.  

    def check_scan_complete(self):

        """Check if the scan is complete."""

        # Add a small delay (e.g., 50ms) before checking the scan status

        time.sleep(0.05)

       

        start_time = time.time()  # Start time for measuring execution duration

        try:

            # Call the ScanIsComplete function to check if scanning is done

            scan_complete = scanner_api.ScanIsComplete()

           

            # Measure elapsed time

            elapsed_time = time.time() - start_time

           

            # Check if the call took too long

            if elapsed_time > 0.1:  # Ensure it completes within 100ms

                self.show_message("Scan completion check took too long.")

                return False

           

            self.show_message(f"Scan complete status: {scan_complete}")

            return scan_complete  # Returns true if scanning is complete

        except Exception as e:

            self.show_message(f"Error in ScanIsComplete: {str(e)}")

            return False

[ElliotG]

There are 2 things you will to change.

1) To achieve your initial pause, instead of a sleep split the method into 2 parts.  Something like:

def check_scan_complete(self):

    Clock.schedule_once(_continue_check_scan_complete, 0.05)

def _continue_scan_complete(self, dt):

    ...the code to read your scanner...

2) In order to have the scan execute concurrently with the event loop, you will want to put the scan into a seperate thread.   

See: https://docs.python.org/3/library/threading.html

The docs are good reference material, but dense.  The first examples should be helpful: https://pymotw.com/3/threading/index.html