usb_serial not working

am using following code



// Automatic FlutterFlow imports
import '/backend/schema/structs/index.dart';
import '/flutter_flow/flutter_flow_theme.dart';
import '/flutter_flow/flutter_flow_util.dart';
import '/custom_code/widgets/index.dart'; // Imports other custom widgets
import '/custom_code/actions/index.dart'; // Imports custom actions
import '/flutter_flow/custom_functions.dart'; // Imports custom functions
import 'package:flutter/material.dart';
// Begin custom widget code
// DO NOT REMOVE OR MODIFY THE CODE ABOVE!

import 'dart:async';
import 'dart:typed_data';
import 'package:usb_serial/transaction.dart';
import 'package:usb_serial/usb_serial.dart';

////////////

class USBSerialWidget extends StatefulWidget {
  const USBSerialWidget({
    Key? key,
    this.width,
    this.height,
    required this.rebuildpage,
  }) : super(key: key);

  final double? width;
  final double? height;
  final Future<dynamic> Function() rebuildpage;

  @override
  _USBSerialWidgetState createState() => _USBSerialWidgetState();
}

////////////

class _USBSerialWidgetState extends State<USBSerialWidget> {
  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(
          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 Scaffold(
      body: Center(
        child: Column(
          children: <Widget>[
            ..._ports,
            Text('Status: $_status\n'),
            ..._serialData,
          ],
        ),
      ),
    );
  }
}

// Automatic FlutterFlow imports
import '/backend/schema/structs/index.dart';
import '/flutter_flow/flutter_flow_theme.dart';
import '/flutter_flow/flutter_flow_util.dart';
import '/custom_code/actions/index.dart'; // Imports other custom actions
import '/flutter_flow/custom_functions.dart'; // Imports custom functions
import 'package:flutter/material.dart';
// Begin custom action code
// DO NOT REMOVE OR MODIFY THE CODE ABOVE!

// Set your action name, define your arguments and return parameter,
// and then add the boilerplate code using the green button on the right!

import 'package:permission_handler/permission_handler.dart';

Future<void> requestPermissions() async {
  await Permission.location.request();
  // await Permission.usb.request();
  await Permission.notification.request();
}