I want to build a simple Android app, like PushOver app, that has a TCP server and receive text messages which it logs and then send them as push notifications. This part is already done and working fine. But I want to receive messages even if the GUI app is closed. I know that this is possible because PushOver app does it ! I gues, I may need a service… but I don’t know how to make one, because this is my firs Andoroid app. As a development environment I use BeeWare(Toga/Briefcase) and Python on a Kubuntu machine. I activated the USB Debuging on the phone and I run the code directly on Android.

app.py

import toga
from toga.style import Pack
from toga.style.pack import COLUMN, ROW

import threading, socket


Debug = True

# ----- Color codes ----------------------

RED        = '33[31m'
GREEN      = '33[32m'
YELLOW     = '33[33m'
MAGENTA    = '33[35m'
CYAN       = '33[36m'
WHITE      = '33[37m'
EXCEPT     = '33[38;5;147m'  # light purple
RESET      = '33[0m'
EventColor = ['', GREEN, YELLOW, RED]


class TCPServer(threading.Thread):
    
  def __init__(self, app):
    super().__init__()
    self.daemon = True
    self.app = app
    self.terminated = threading.Event()
    self.start()

  def Terminate(self):
    if self.is_alive():
      self.terminated.set()
      with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as ESocket:
        try:
          ESocket.settimeout(0.2)
          ESocket.connect(('localhost', 12345))
        except: pass
      self.join()
      
  def run(self):    
    def HandleClient(Conn):
      with Conn:
        message = Conn.recv(1024).decode()
        if not message: return
        self.app.loop.call_soon_threadsafe(self.app.LogMessage, message)
        #self.app.SendNotif(message)

    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as SSocket:
      try:
        SSocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        SSocket.bind(('192.168.0.21', 12345))
        SSocket.listen(10)
        if Debug:
          print(GREEN + 'TCP Server is listening on port 12345...' + RESET)
        try:
          while not self.terminated.is_set():
            Conn, Addr = SSocket.accept()
            if self.terminated.is_set():
              Conn.close(); break
            HandleClient(Conn)
        except Exception as E1:
          if Debug: print(RED + f'TCP Server exception (listen): {E1}' + RESET)
        finally:
          if Debug: print(YELLOW + 'TCP Server has stopped listening.' + RESET)
      except Exception as E2:
        if Debug: print(RED + f'TCP Server exception (setup): {E2}' + RESET)
        

class Application(toga.App):
    
  def startup(self):
    self.on_exit = self.exit_handler  
    self.main_window = toga.MainWindow(title=self.formal_name)
    self.log = toga.MultilineTextInput(readonly=True, style=Pack(flex=1))
    main_box = toga.Box(children=[self.log], style=Pack(direction=COLUMN, padding=10))
    self.main_window.content = main_box
    self.main_window.show()
    self.tcp_server = TCPServer(self)

  def exit_handler(self, app):
    try:  
      self.tcp_server.Terminate()
    finally:  
      return True

  def LogMessage(self, message):
    self.log.value += message + 'n'

  def SendNotif(self, message):
    self.main_window.info_dialog('New Message', message)


def main():
    return Application()