Building a Countdown Timer in Flutter

animated_count_down_timer.dart

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

void main() {
  runApp(const 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.deepPurple,
      ),
      home: const TimerScreen(),
    );
  }
}

class TimerScreen extends StatefulWidget {
  const TimerScreen({Key? key}) : super(key: key);

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

class _TimerScreenState extends State<TimerScreen> {
  static const Duration countdownDuration = Duration(minutes: 0, seconds: 10);
  final ValueNotifier<Duration> durationNotifier =
      ValueNotifier<Duration>(countdownDuration);
  Timer? timer;

  @override
  void initState() {
    super.initState();
    startTimer();
  }

  @override
  void dispose() {
    timer?.cancel();
    durationNotifier.dispose();
    super.dispose();
  }

  void startTimer() {
    timer = Timer.periodic(const Duration(seconds: 1), (_) => addTime());
  }

  void addTime() {
    final seconds = durationNotifier.value.inSeconds - 1;
    if (seconds < 0) {
      timer?.cancel();
      // Handle end of timer here
      showEndMessage();
    } else {
      durationNotifier.value = Duration(seconds: seconds);
    }
  }

  void showEndMessage() {
    showDialog(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          title: const Text("Timer Ended"),
          content: const Text("The timer has ended."),
          actions: <Widget>[
            TextButton(
              child: const Text("OK"),
              onPressed: () {
                Navigator.of(context).pop();
              },
            ),
          ],
        );
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: _onWillPop,
      child: Scaffold(
        backgroundColor: const Color(0xFFadd8e6),
        body: Center(
          child: ValueListenableBuilder<Duration>(
            valueListenable: durationNotifier,
            builder: (context, duration, child) {
              return Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  buildTime(duration),
                  if (duration.inSeconds <= 0) // Show "END" when timer is zero or less
                    const Padding(
                      padding: EdgeInsets.only(top: 20.0),
                      child: Text(
                        "END",
                        style: TextStyle(
                          color: Colors.white,
                          fontSize: 36,
                          fontWeight: FontWeight.bold,
                        ),
                      ),
                    ),
                ],
              );
            },
          ),
        ),
      ),
    );
  }

  Future<bool> _onWillPop() async {
    timer?.cancel();
    Navigator.of(context).pop();
    return true;
  }

  Widget buildTime(Duration duration) {
    String twoDigits(int n) => n.toString().padLeft(2, '0');
    final hours = twoDigits(duration.inHours);
    final minutes = twoDigits(duration.inMinutes.remainder(60));
    final seconds = twoDigits(duration.inSeconds.remainder(60));

    return Row(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        buildTimeColumn(hours, "Hrs"),
        buildTimeColumn(minutes, "Mins"),
        buildTimeColumn(seconds, "Secs", isLast: true),
      ],
    );
  }

  Widget buildTimeColumn(String time, String label, {bool isLast = false}) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Row(
          children: [
            buildDigit(time[0]),
            buildDigit(time[1]),
            if (!isLast) buildTimeSeparator(),
          ],
        ),
        buildLabel(label),
      ],
    );
  }

  Widget buildDigit(String digit) {
    return Container(
      padding: const EdgeInsets.symmetric(horizontal: 20, vertical: 4),
      margin: const EdgeInsets.symmetric(horizontal: 2),
      decoration: BoxDecoration(
        color: Colors.white,
        borderRadius: BorderRadius.circular(8),
      ),
      child: ClipRect(
        child: AnimatedSwitcher(
          duration: const Duration(milliseconds: 600),
          switchInCurve: Curves.easeOutExpo,
          switchOutCurve: Curves.easeInExpo,
          transitionBuilder: (Widget child, Animation<double> animation) {
            return Stack(
              children: <Widget>[
                SlideTransition(
                  position: Tween<Offset>(
                    begin: const Offset(0, -1),
                    end: const Offset(0, 1),
                  ).animate(CurvedAnimation(
                    parent: animation,
                    curve: Curves.easeOutCubic,
                  )),
                  child: FadeTransition(
                    opacity: animation,
                    child: child,
                  ),
                ),
                SlideTransition(
                  position: Tween<Offset>(
                    begin: const Offset(0, -1),
                    end: const Offset(0, 0),
                  ).animate(CurvedAnimation(
                    parent: animation,
                    curve: Curves.bounceIn,
                  )),
                  child: FadeTransition(
                    opacity: animation,
                    child: child,
                  ),
                ),
              ],
            );
          },
          child: Text(
            digit,
            key: ValueKey<String>(digit),
            style: const TextStyle(
              fontWeight: FontWeight.bold,
              color: Colors.black,
              fontSize: 50,
            ),
          ),
        ),
      ),
    );
  }

  Widget buildLabel(String label) {
    return Text(
      label,
      style: const TextStyle(
        color: Colors.white,
        fontSize: 20,
        fontWeight: FontWeight.bold,
      ),
    );
  }

  Widget buildTimeSeparator() {
    return const Padding(
      padding: EdgeInsets.symmetric(horizontal: 2.0),
      child: Text(
        ":",
        style: TextStyle(
          color: Colors.white,
          fontSize: 50,
        ),
      ),
    );
  }
}