Helper to do async methods in other thread in flutter

async_helper.dart

import 'dart:isolate';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

enum AsyncState { idle, loading, running }

class AsyncMessage {
  final Function asyncMethod;
  List data;
  SendPort sendPort;

  AsyncMessage(this.asyncMethod, this.data, this.sendPort);
}

class AsyncManager {
  final Function asyncMethod;
  final Function(dynamic message) onSuccess;
  final Function onError;

  final ReceivePort _receivePort;
  final ReceivePort _errorPort;
  Isolate _isolate;
  AsyncState _state = AsyncState.idle;
  AsyncState get state => _state;
  bool get isRunning => _state != AsyncState.idle;

  AsyncManager({@required this.asyncMethod, this.onSuccess, this.onError})
      : assert(asyncMethod != null),
        _receivePort = ReceivePort(),
        _errorPort = ReceivePort() {
    _receivePort.listen(_receiveMessage, onError: _receiveMessage);
    _errorPort.listen(_errorMessage);
  }

  void start(List data) {
    if (!isRunning) {
      _state = AsyncState.loading;
      _run(data);
    }
  }

  void stop() {
    if (isRunning) {
      _state = AsyncState.idle;
      if (_isolate != null) {
        _isolate.kill(priority: Isolate.immediate);
        _isolate = null;
      }
    }
  }

  void _errorMessage(dynamic message) {
    stop();
    onError?.call(message);
  }

  void _run(List data) {
    if (isRunning) {
      final AsyncMessage message = AsyncMessage(asyncMethod, data, _receivePort.sendPort);
      Isolate.spawn<AsyncMessage>(_execute, message, onError: _errorPort.sendPort).then((Isolate isolate) {
        if (!isRunning) {
          isolate.kill(priority: Isolate.immediate);
        } else {
          _state = AsyncState.running;
          _isolate = isolate;
        }
      });
    }
  }

  void _receiveMessage(dynamic message) {
    onSuccess?.call(message);
  }

  static void _execute(AsyncMessage message) async{
    final SendPort sender = message.sendPort;
    var result = await Function.apply(message.asyncMethod, message.data);
    sender.send(result);
  }
}