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Android app crashes because don't found characteristic

See original GitHub issue

bleak version: 0.14.3
Python version: 3.9.12
Operating System: Android 6.0.1, API 23

I am trying to get this android app to work which is supposed to connect to a Mi Smart Scale 2 scale via low energy Bluetooth. However, even if the app crashes from the logs I see that it connects to the phone.

The app once connected to the phone should read the feature with the start_notify operation but this does not happen.

This is the error that I get, from logcat in android studio:

022-06-13 17:34:33.657 12975-12986/org.test.demo12 D/BluetoothGatt: onClientConnParamsChanged() - Device=70:87:9E:0F:F8:7D interval=39 status=0
2022-06-13 17:34:33.847 12975-13001/org.test.demo12 I/python: Connected: True
2022-06-13 17:34:33.847 12975-13001/org.test.demo12 D/BluetoothGatt: cancelOpen() - device: 70:87:9E:0F:F8:7D
2022-06-13 17:34:33.847 1944-1978/? D/BtGatt.GattService: clientDisconnect() - address=70:87:9E:0F:F8:7D, connId=10
2022-06-13 17:34:33.847 1944-2370/? E/bt_btm: btm_ble_get_search_if search_if=4
2022-06-13 17:34:33.847 1944-2370/? W/bt_btif: bta_gattc_conn_cback() - cif=4 connected=0 conn_id=4 reason=0x0016
2022-06-13 17:34:33.847 1944-2370/? W/bt_btif: bta_gattc_conn_cback() - cif=5 connected=0 conn_id=5 reason=0x0016
2022-06-13 17:34:33.847 1944-2370/? W/bt_btif: bta_gattc_conn_cback() - cif=6 connected=0 conn_id=6 reason=0x0016
2022-06-13 17:34:33.847 1944-2370/? W/bt_btif: bta_gattc_conn_cback() - cif=7 connected=0 conn_id=7 reason=0x0016
2022-06-13 17:34:33.847 1944-2370/? W/bt_btif: bta_gattc_conn_cback() - cif=8 connected=0 conn_id=8 reason=0x0016
2022-06-13 17:34:33.847 1944-2370/? W/bt_btif: bta_gattc_conn_cback() - cif=9 connected=0 conn_id=9 reason=0x0016
2022-06-13 17:34:33.847 1944-2370/? W/bt_btif: bta_gattc_conn_cback() - cif=10 connected=0 conn_id=10 reason=0x0016
2022-06-13 17:34:33.857 1944-2267/? D/bt_vendor: op for 7
2022-06-13 17:34:33.857 1944-2267/? D/bt_upio: upio_set : pio 0 action 2, polarity 1
2022-06-13 17:34:33.857 1944-2267/? D/bt_upio: BT_WAKE is asserted already
2022-06-13 17:34:33.857 1944-2370/? E/bt_btif: bta_gattc_mark_bg_conn unable to find the bg connection mask for: 70:87:9e:0f:f8:7d
2022-06-13 17:34:33.857 1944-2113/? D/BtGatt.GattService: onDisconnected() - clientIf=10, connId=10, address=70:87:9E:0F:F8:7D
2022-06-13 17:34:33.857 12975-12987/org.test.demo12 D/BluetoothGatt: onClientConnectionState() - status=0 clientIf=10 device=70:87:9E:0F:F8:7D
2022-06-13 17:34:33.857 844-2748/? V/AlarmManager:  remove PendingIntent] PendingIntent{c6946a9: PendingIntentRecord{96e10 com.android.bluetooth broadcastIntent}}
2022-06-13 17:34:33.857 844-1752/? V/AlarmManager:  remove PendingIntent] PendingIntent{c10c42e: PendingIntentRecord{96e10 com.android.bluetooth broadcastIntent}}
2022-06-13 17:34:33.867 12975-13001/org.test.demo12 D/BluetoothGatt: close()
2022-06-13 17:34:33.867 12975-13001/org.test.demo12 D/BluetoothGatt: unregisterApp() - mClientIf=10
2022-06-13 17:34:33.867 1944-7183/? D/BtGatt.GattService: unregisterClient() - clientIf=10
2022-06-13 17:34:33.867 12975-13001/org.test.demo12 I/python:  Traceback (most recent call last):
2022-06-13 17:34:33.867 12975-13001/org.test.demo12 I/python:    File "/content/.buildozer/android/app/main.py", line 225, in <module>
2022-06-13 17:34:33.867 12975-13001/org.test.demo12 I/python:    File "/content/.buildozer/android/platform/build-armeabi-v7a/build/other_builds/python3/armeabi-v7a__ndk_target_21/python3/Lib/asyncio/base_events.py", line 616, in run_until_complete
2022-06-13 17:34:33.867 12975-13001/org.test.demo12 I/python:    File "/content/.buildozer/android/app/main.py", line 218, in get_the_weight_from_the_mi_smart_scale_2
2022-06-13 17:34:33.867 12975-13001/org.test.demo12 I/python:    File "/content/.buildozer/android/platform/build-armeabi-v7a/build/python-installs/demo12/armeabi-v7a/bleak/backends/p4android/client.py", line 486, in start_notify
2022-06-13 17:34:33.867 12975-13001/org.test.demo12 I/python:  bleak.exc.BleakError: Characteristic with UUID 00002a9d-0000-1000-8000-00805f9b34fb could not be found!
2022-06-13 17:34:33.867 12975-13001/org.test.demo12 I/python: Python for android ended.
2022-06-13 17:34:33.897 1944-2370/? I/bt_btm_sec: btm_sec_disconnected clearing pending flag handle:64 reason:22

This is the code I converted with Colab:

import asyncio

from kivy.app import App
from kivy.lang.builder import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.properties import ObjectProperty

from bleak import BleakClient


kv = '''
WindowManager:
    
    MainWindow:
    BluetoothWindow:
    LoginWindow:
    
        
     
    
<LoginWindow>:
    name: "login"

    email: email
    password: password

    FloatLayout:

        Label:
            text:"Email: "
            font_size: (root.width**2 + root.height**2) / 13**4
            pos_hint: {"x":0.1, "top":0.9}
            size_hint: 0.35, 0.15

        TextInput:
            id: email
            font_size: (root.width**2 + root.height**2) / 13**4
            multiline: False
            pos_hint: {"x": 0.45 , "top":0.9}
            size_hint: 0.4, 0.15

        Label:
            text:"Password: "
            font_size: (root.width**2 + root.height**2) / 13**4
            pos_hint: {"x":0.1, "top":0.7}
            size_hint: 0.35, 0.15

        TextInput:
            id: password
            font_size: (root.width**2 + root.height**2) / 13**4
            multiline: False
            password: True
            pos_hint: {"x": 0.45, "top":0.7}
            size_hint: 0.4, 0.15

        Button:
            pos_hint:{"x":0.2,"y":0.05}
            size_hint: 0.6, 0.2
            font_size: (root.width**2 + root.height**2) / 13**4
            text: "Login"
            on_release:
                app.root.current = "main"
                root.manager.transition.direction = "left"

        Button:
            pos_hint:{"x":0.2,"y":0.3}
            size_hint: 0.6, 0.1
            font_size: (root.width**2 + root.height**2) / 17**4
            text: "Non hai un account? Creane uno"  
            on_release:
     
                
     
        
     
<MainWindow>:
    name: "main"
    BoxLayout:
		orientation: "vertical"
		size: root.width, root.height
        
    FloatLayout:
        n: n
        email: email
        created:created

        FloatLayout:
            Label:
                id: n
                pos_hint:{"x": 0.1, "top":0.9}
                size_hint:0.8, 0.2
                text: "Nome account: "

            Label:
                id: email
                pos_hint:{"x": 0.1, "top":0.7}
                size_hint:0.8, 0.2
                text: "Email: "

            Label:
                id: created
                pos_hint:{"x": 0.1, "top":0.5}
                size_hint:0.8, 0.2
                text: "Creato il: "

            Button:
                pos_hint:{"x":0.35, "y": 0.2}
                size_hint:0.3,0.1
                text: "Log Out"
                on_release:
                    app.root.current = "login"
                    root.manager.transition.direction = "right"
                

            Button:
                pos_hint:{"x":0.35, "y": 0.1}
                size_hint:0.3,0.1
                text: "Log In"
                on_release:
                    app.root.current = "ble"
                    root.manager.transition.direction = "left"
                
<BluetoothWindow>:
    name: "ble"
    peso: peso

    
    BoxLayout:
		orientation: "vertical"
		size: root.width, root.height

    FloatLayout:
        Label:
            id: peso
            pos_hint:{"x": 0.1, "top":0.7}
            size_hint:0.8, 0.2
            text: "peso: "
        
        Button:
            pos_hint:{"x":0.2, "y": 0.1}
            size_hint:0.6,0.2
            text: "Log Out"
            on_release:
                app.root.current = "main"
                root.manager.transition.direction = "right"
'''

class LoginWindow(Screen):
    pass

class MainWindow(Screen):
    pass

class BluetoothWindow(Screen):
    peso = ObjectProperty(None)
    
    def on_enter(self):

        self.peso.text = "peso: " + str(data2)


class WindowManager(ScreenManager):
    pass

sm = WindowManager()

screens = [MainWindow(name="main"), 
           BluetoothWindow(name="ble"),
           LoginWindow(name="login")]

for screen in screens:
    sm.add_widget(screen)


sm.current = "main"

class AsyncApp(App):

    other_task = None

    def build(self):
        return Builder.load_string(kv)
    
    def build2(self):
        return sm

    def app_func(self):
        '''This will run both methods asynchronously and then block until they
        are finished
        '''
        self.other_task = asyncio.ensure_future(self.get_the_weight_from_the_mi_smart_scale_2())

        async def run_wrapper():
            # we don't actually need to set asyncio as the lib because it is
            # the default, but it doesn't hurt to be explicit
            await self.async_run(async_lib='asyncio')
            print('App done')
            self.other_task.cancel()

        return asyncio.gather(run_wrapper(), self.other_task)
   
    global notification_handler
    def notification_handler(sender, data):
        """Simple notification handler which prints the data received."""
        data1 = list(data)
        global data2
        data2 = ((data1[1]+data1[2]*256)*0.005)
        print("{0}: {1}".format(sender, data2))

    async def get_the_weight_from_the_mi_smart_scale_2(self):
        #da modificare
        '''This method is also run by the asyncio loop and periodically prints
        something.
        '''
        async with BleakClient("70:87:9E:0F:F8:7D") as client:
            print(f"Connected: {client.is_connected}")
            
            await client.start_notify("00002a9d-0000-1000-8000-00805f9b34fb", notification_handler)
            await asyncio.sleep(30.0)
            await client.stop_notify("00002a9d-0000-1000-8000-00805f9b34fb")   


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(AsyncApp().app_func())
    loop.close()