Experimenting on Stream with isolates in flutter

main.dart

import 'dart:async';
import 'dart:isolate';

import 'package:flutter/material.dart';

void computeIsolate(Message message) {
  Stream<int> streamcompute(numb) async* {
    for (var i = 0; i < numb; i++) {
      yield i;
    }
  }

  final StreamController _controller = StreamController.broadcast();

  _controller.addStream(streamcompute(message.numb));

  _controller.stream.listen((event) {
    message.sendPort.send(event);
  });

  // streamcompute(message.numb).listen((event) {
  //   message.sendPort.send(event);
  // });
}

void main() async {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  final receivePort = ReceivePort();
  Isolate? isolate;
  List list = <ListTile>[];
  @override
  void initState() {
    super.initState();
    Future.microtask(() async {
      isolate = await Isolate.spawn(
        computeIsolate,
        Message(sendPort: receivePort.sendPort, numb: 20),
      );

      list = [];

      receivePort.listen((message) {
        print(message);
      }).onData((data) {
        list.add(ListTile(
            title: Text("First message from isolate stream is $data")));
      });
    });
  }

  @override
  void dispose() {
    isolate?.kill();
    super.dispose();
  }

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: SingleChildScrollView(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
            Container(
              height: 700,
              alignment: Alignment.center,
              child: ListView.builder(
                itemCount: 20,
                itemBuilder: (context, index) {
                  if (list.isNotEmpty) {
                    return list[index];
                  } else {
                    return const Text('isolate did not run');
                  }
                },
              ),
            )
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class Message {
  Message({
    required this.numb,
    required this.sendPort,
  });
  int numb;
  SendPort sendPort;
}