flutter_hooks reproducer

main.dart

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

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

enum ChildType { a, b }

class ChildState<T> {
  final Stream<T> childStream;
  final ChildType childType;
  ChildState(this.childStream, this.childType);
}

Stream<String> aStream() {
  return Stream.periodic(const Duration(milliseconds: 500), (i) => 'EventA');
}

Stream<String> bStream() {
  return Stream.periodic(const Duration(milliseconds: 500), (i) => 'EventB');
}

Stream<ChildState> stream() {
  return Stream.periodic(const Duration(seconds: 1), (i) {
    return i % 2 == 0
        ? ChildState(aStream(), ChildType.a)
        : ChildState(bStream(), ChildType.b);
  });
}

class MyApp extends HookWidget {
  static final _stream = stream();

  @override
  Widget build(BuildContext context) {
    final snapshot = useStream(_stream);

    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
            child: snapshot.hasData
                ? ChildStatusWidget(snapshot.requireData)
                : const CircularProgressIndicator()),
      ),
    );
  }
}

class ChildStatusWidget extends HookWidget {
  final ChildState state;

  const ChildStatusWidget(this.state);

  @override
  Widget build(BuildContext context) {
    final preserveState = useState(true);
    final snapshot =
        useStream(state.childStream,
                  preserveState: preserveState.value);

    return Column(children: [
      Text(
        'Hello, World! ${state.childType} ${snapshot.data}',
        style: Theme.of(context).textTheme.headline4,
      ),
      ElevatedButton(
          child: Text('PreserveState: ${preserveState.value}'),
          onPressed: () {
            preserveState.value = !preserveState.value;
          }),
    ]);
  }
}