Async expand example

main.dart

/*
 * Stream async expand
 * https://gist.github.com/PlugFox/0366eb6d7bd2f3e03fd629c5a96ea8ff
 * https://dartpad.dev?id=0366eb6d7bd2f3e03fd629c5a96ea8ff
 * Mike Matiunin <plugfox@gmail.com>, 07 March 2024
 */

import 'dart:async';

import 'package:flutter/material.dart';

typedef Product = String;
typedef Property = String;
typedef Row = ({Product product, List<Property> properties});

final List<Row> data = <Row>[
  (product: 'banana', properties: ['yellow', 'tasty', 'long']),
  (product: 'apple', properties: ['red', 'juicy']),
  (product: 'cherry', properties: ['red', 'sweet', 'small']),
];

void main() {
  final state = <Product, Row>{};

  Future<void> delay([int ms = 1000]) => Future<void>.delayed(Duration(milliseconds: ms));

  final stream = Stream<Row>.fromIterable(data)
      .asyncExpand((e) async* {
        yield (product: e.product, properties: <Property>[]);
        for (var i = 0; i < e.properties.length; i++) {
          await delay();
          yield (product: e.product, properties: e.properties.sublist(0, i + 1));
        }
      })
      .map((row) => state..[row.product] = row)
      .map((state) => state.values.toList(growable: false));

  runZonedGuarded<void>(
    () => runApp(App(stream: stream)),
    (error, stackTrace) => print('Top level exception: error\nstackTrace'), // ignore: avoid_print
  );
}

class App extends StatelessWidget {
  const App({required this.stream, super.key});

  final Stream<List<Row>> stream;

  @override
  Widget build(BuildContext context) => MaterialApp(
        title: 'Async Expand Example',
        theme: ThemeData.dark(),
        home: Scaffold(
          appBar: AppBar(
            title: const Text('Async Expand Example'),
          ),
          body: SafeArea(
            child: StreamBuilder<List<Row>>(
              stream: stream,
              builder: (context, snapshot) {
                final data = snapshot.data ?? <Row>[];
                return ListView.builder(
                  itemCount: data.length,
                  itemBuilder: (context, index) {
                    final row = data[index];
                    return ListTile(
                      title: Text(row.product),
                      subtitle: Text('[${row.properties.join(', ')}]'),
                    );
                  },
                );
              },
            ),
          ),
        ),
      );
}