Using an Isolate in Flutter

main.dart

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Isolate Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Isolates'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Isolate _isolate;
  bool _running = false;
  static int _counter = 0;
  String notification = "";
  ReceivePort _receivePort;
 
  void _start() async {
    _running = true;
    _receivePort = ReceivePort();
    _isolate = await Isolate.spawn(_checkTimer, _receivePort.sendPort);
    _receivePort.listen(_handleMessage, onDone:() {
        print("done!");
    });
  }

  static void _checkTimer(SendPort sendPort) async {
    Timer.periodic(new Duration(seconds: 1), (Timer t) {
      _counter++;
      String msg = 'notification ' + _counter.toString();      
      print('SEND: ' + msg);
      sendPort.send(msg);
    });
  }

  void _handleMessage(dynamic data) {
    print('RECEIVED: ' + data);
    setState(() {      
      notification = data;
    });
  }

  void _stop() {
    if (_isolate != null) {
      setState(() {
          _running = false; 
          notification = '';   
      });
      _receivePort.close();
      _isolate.kill(priority: Isolate.immediate);
      _isolate = null;        
      }
  }


  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Text(
              notification,
            ),
          ],
        ),
      ),
      floatingActionButton: new FloatingActionButton(
        onPressed: _running ? _stop : _start,
        tooltip: _running ? 'Timer stop' : 'Timer start',
        child: _running ? new Icon(Icons.stop) : new Icon(Icons.play_arrow),
      ),
      );
  }
}

Hello! Thanks for sharing this! I was having difficulties to run a simple timer in background. Your sample code was useful! Based on it, I created this counter with the possibility to pass an initial time as parameter. I hope this can help other people too.

import 'dart:async';  
import 'dart:isolate';  
  
class CountdownTimer {  
  final receivePort = ReceivePort();  
  Isolate _isolate;  
  
 void stop() {  
    receivePort.close();  
  _isolate.kill(priority: Isolate.immediate);  
  }  
  
  Future<void> start(Duration initialDuration) async {  
    Map map = {  
      'port': receivePort.sendPort,  
  'initial_duration': initialDuration,  
  };  
  _isolate = await Isolate.spawn(_entryPoint, map);  
  receivePort.sendPort.send(initialDuration);  
  }  
  
  static void _entryPoint(Map map) async {  
    Duration initialTime = map['initial_duration'];  
  SendPort port = map['port'];  
  
  Timer.periodic(  
      Duration(seconds: 1),  
  (timer) {  
        if (timer.tick == initialTime.inSeconds) {  
          timer.cancel();  
  port.send(timer.tick);  
  port.send('Timer finished');  
  } else {  
          port.send(timer.tick);  
  }  
      },  
  );  
  }  
}