Cannot find StreamZip or StreamGroup

Question

I cannot use StreamGroup or StreamZip for some reason

here's the code (that is complete useless, but I don't want to anger the admins)

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

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

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

  @override
  Widget build(BuildContext context) => const MaterialApp(home: MyHomePage());
}

class MyHomePage extends StatefulWidget {
  const MyHomePage() : super(key: const Key('MyHomePage'));

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

class _MyHomePageState extends State<MyHomePage> {
  static const _duration = Duration(seconds: 3);
  static const _initialCx = 3.0;

  final _pageStream = Stream<int>.periodic(_duration, (int i) => i);

  ScrollController _scrollController;
  StreamController<double> _throttle;
  

  @override
  void initState() {
    _scrollController = ScrollController();
    _throttle = StreamController();

    StreamGroup<num>.merge([_pageStream, _throttle.stream]); // <= this

    StreamZip([_pageStream, _throttle.stream]); //  or this

    /// i NEED TO IMPLEMENT A LISTENER HERE... THE CODE IS USELESS OTHERWISE

    super.initState();
  }

  @override
  void dispose() {
    _scrollController?.dispose();
    _throttle?.close();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) => Scaffold(
        body: Stack(children: <Widget>[
          ListView.builder(
            controller: _scrollController,
            itemBuilder: (BuildContext context, int index) => const Center(
              child: FlutterLogo(size: 160),
            ),
          ),
          Align(
            alignment: Alignment.bottomCenter,
            child: StreamBuilder<double>(
              builder: (context, throttle) => Slider(
                min: 1,
                max: 5,
                onChanged: (double value) => _throttle.sink.add(value),
                value: throttle.data ?? _initialCx,
              ),
            ),
          ),
        ]),
      );
}

here are the errors respectively for

StreamZip

The method 'StreamZip' isn't defined for the type '_MyHomePageState'. Try correcting the name to the name of an existing method, or defining a method named 'StreamZip'.

SteamGroup

The name 'StreamGroup' isn't a class. Try correcting the name to match an existing class.

I admittedly don't have much experience with those classes, so the solution might be trivial,

can you please explain me how do I access those?

Thank you

Lazaro

Answer 1

It's not obvious due to the way that the Flutter API documentation merges everything together, but StreamZip and StreamGroup come from package:async, not from dart:async. You'll need to replace import 'dart:async'; with import 'package:async/async.dart'; and add an async dependency in your pubspec.yaml file.

(Even though package:async is from the Dart developers, it's separate from dart:async because:

• The classes and functions in package:async aren't considered to be core parts of the Dart SDK.
• package:async can be implemented in pure Dart code.
• A separate package can be updated separately from the Dart SDK, allowing for more frequent updates.)

Afghani