auto connect usb device, arduino

Question

I have android 10 installed on my raspberry Pi 3b +. I want to be able to transfer data to arduino using serial port. I used an example application written in a flutter. Everything works fine, devices are displayed and you can connect to them directly. I send a specific value, and arduino reads it and executes the appropriate command. My point is that when you start the application in the flutter, it automatically connects to the arduino device through the serial port. I don't want a list with a selection and buttons to connect, just automatic. How should I do this please help.

below the code for my main.dart

import 'dart:async';
import 'dart:typed_data';

import 'package:flutter/material.dart';
import 'package:usb_serial/transaction.dart';
import 'package:usb_serial/usb_serial.dart';

void main() => runApp(MyApp());

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  UsbPort? _port;
  String _status = "Idle";
  List<Widget> _ports = [];
  List<Widget> _serialData = [];

  StreamSubscription<String>? _subscription;
  Transaction<String>? _transaction;
  UsbDevice? _device;

  TextEditingController _textController = TextEditingController();

  Future<bool> _connectTo(device) async {
    _serialData.clear();

    if (_subscription != null) {
      _subscription!.cancel();
      _subscription = null;
    }

    if (_transaction != null) {
      _transaction!.dispose();
      _transaction = null;
    }

    if (_port != null) {
      _port!.close();
      _port = null;
    }

    if (device == null) {
      _device = null;
      setState(() {
        _status = "Disconnected";
      });
      return true;
    }

    _port = await device.create();
    if (await (_port!.open()) != true) {
      setState(() {
        _status = "Failed to open port";
      });
      return false;
    }
    _device = device;

    await _port!.setDTR(true);
    await _port!.setRTS(true);
    await _port!.setPortParameters(115200, UsbPort.DATABITS_8, UsbPort.STOPBITS_1, UsbPort.PARITY_NONE);

    _transaction = Transaction.stringTerminated(_port!.inputStream as Stream<Uint8List>, Uint8List.fromList([13, 10]));

    _subscription = _transaction!.stream.listen((String line) {
      setState(() {
        _serialData.add(Text(line));
        if (_serialData.length > 20) {
          _serialData.removeAt(0);
        }
      });
    });

    setState(() {
      _status = "Connected";
    });
    return true;
  }

  void _getPorts() async {
    _ports = [];
    List<UsbDevice> devices = await UsbSerial.listDevices();
    if (!devices.contains(_device)) {
      _connectTo(null);
    }
    print(devices);

    devices.forEach((device) {
      _ports.add(ListTile(
          leading: Icon(Icons.usb),
          title: Text(device.productName!),
          subtitle: Text(device.manufacturerName!),
          trailing: ElevatedButton(
            child: Text(_device == device ? "Disconnect" : "Connect"),
            onPressed: () {
              _connectTo(_device == device ? null : device).then((res) {
                _getPorts();
              });
            },
          )));
    });

    setState(() {
      print(_ports);
    });
  }

  @override
  void initState() {
    super.initState();

    UsbSerial.usbEventStream!.listen((UsbEvent event) {
      _getPorts();
    });

    _getPorts();
  }

  @override
  void dispose() {
    super.dispose();
    _connectTo(null);
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        home: Scaffold(
          appBar: AppBar(
            title: const Text('USB Serial Plugin example app'),
          ),
          body: Center(
              child: Column(children: <Widget>[
                Text(_ports.length > 0 ? "Available Serial Ports" : "No serial devices available", style: Theme.of(context).textTheme.headline6),
                ..._ports,
                Text('Status: $_status\n'),
                Text('info: ${_port.toString()}\n'),
                ListTile(
                  title: TextField(
                    controller: _textController,
                    decoration: InputDecoration(
                      border: OutlineInputBorder(),
                      labelText: 'Text To Send',
                    ),
                  ),
                  trailing: ElevatedButton(
                    child: Text("Send"),
                    onPressed: _port == null
                        ? null
                        : () async {
                      if (_port == null) {
                        return;
                      }
                      String data = _textController.text + "\r\n";
                      await _port!.write(Uint8List.fromList(data.codeUnits));
                      _textController.text = "";
                    },
                  ),
                ),
                Text("Result Data", style: Theme.of(context).textTheme.headline6),
                ..._serialData,
              ])),
        ));
  }
}