Riverpod Countdown

main.dart

import 'dart:async';

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

void main() {
  runApp(const ProviderScope(child: 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 HomePage(),
    );
  }
}

class HomePage extends ConsumerWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final countdown = ref.watch(countdownProvider(15));

    return Material(
      child: Center(
        child: countdown.maybeWhen(
          data: (data) => Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              Text('${data.tick}'),
              Text('${data.countdownState}'),
            ],
          ),
          orElse: () => Container(),
        ),
      ),
    );
  }
}

final countdownProvider =
    StreamProvider.family.autoDispose<Countdown, int>((ref, limit) {
  final stream = Stream<int>.periodic(
    const Duration(seconds: 1),
    (number) => limit - number,
  ).takeWhile((tick) => tick >= 0).map<Countdown>(
        (tick) => Countdown(
          tick: tick,
          countdownState:
              tick > 0 ? CountdownState.inProgress : CountdownState.finished,
        ),
      );

  return stream;
});

class Countdown {
  const Countdown({
    required this.tick,
    required this.countdownState,
  });

  final int tick;
  final CountdownState countdownState;

  @override
  bool operator ==(Object other) {
    if (identical(this, other)) return true;

    return other is Countdown &&
        other.tick == tick &&
        other.countdownState == countdownState;
  }

  @override
  int get hashCode => tick.hashCode ^ countdownState.hashCode;
}

enum CountdownState { inProgress, finished }