Countdown Timer - Part 1

main.dart

import 'dart:async';

import 'package:flutter/material.dart';

const Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(
        scaffoldBackgroundColor: darkBlue,
      ),
      debugShowCheckedModeBanner: false,
      home: Home(),
    );
  }
}

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return const Scaffold(
      body: Center(
        child: Countdown(duration: Duration(seconds: 10)),
      ),
    );
  }
}

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

  final Duration duration;

  @override
  State<Countdown> createState() => _CountdownState();
}

class _CountdownState extends State<Countdown> {
  late int _counter;
  late StreamSubscription _subscription;

  String get _counterText => _counter.toString().padLeft(2, '0');

  void _onTick(event) {
    setState(() {
      _counter = _counter - 1;
    });
  }

  @override
  void initState() {
    _counter = widget.duration.inSeconds;
    _subscription = Stream.periodic(const Duration(seconds: 1))
        .take(widget.duration.inSeconds)
        .listen(_onTick);
    super.initState();
  }

  @override
  void dispose() {
    _subscription.cancel();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Text(
          _counterText,
          style: Theme.of(context).textTheme.headline2,
        ),
      ),
    );
  }
}