Flutter Countdown Timer

Here is an example using Timer.periodic :

Countdown starts from 10 to 0 on button click :

import 'dart:async';

[...]

Timer _timer;
int _start = 10;

void startTimer() {
  const oneSec = const Duration(seconds: 1);
  _timer = new Timer.periodic(
    oneSec,
    (Timer timer) {
      if (_start == 0) {
        setState(() {
          timer.cancel();
        });
      } else {
        setState(() {
          _start--;
        });
      }
    },
  );
}

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

Widget build(BuildContext context) {
  return new Scaffold(
    appBar: AppBar(title: Text("Timer test")),
    body: Column(
      children: <Widget>[
        RaisedButton(
          onPressed: () {
            startTimer();
          },
          child: Text("start"),
        ),
        Text("$_start")
      ],
    ),
  );
}

Result :

Flutter countdown timer example

You can also use the CountdownTimer class from the quiver.async library, usage is even simpler :

import 'package:quiver/async.dart';

[...]

int _start = 10;
int _current = 10;

void startTimer() {
  CountdownTimer countDownTimer = new CountdownTimer(
    new Duration(seconds: _start),
    new Duration(seconds: 1),
  );

  var sub = countDownTimer.listen(null);
  sub.onData((duration) {
    setState(() { _current = _start - duration.elapsed.inSeconds; });
  });

  sub.onDone(() {
    print("Done");
    sub.cancel();
  });
}

Widget build(BuildContext context) {
  return new Scaffold(
    appBar: AppBar(title: Text("Timer test")),
    body: Column(
      children: <Widget>[
        RaisedButton(
          onPressed: () {
            startTimer();
          },
          child: Text("start"),
        ),
        Text("$_current")
      ],
    ),
  );
}

EDIT : For the question in comments about button click behavior

With the above code which uses Timer.periodic, a new timer will indeed be started on each button click, and all these timers will update the same _start variable, resulting in a faster decreasing counter.

There are multiple solutions to change this behavior, depending on what you want to achieve :

disable the button once clicked so that the user could not disturb the countdown anymore (maybe enable it back once timer is cancelled)
wrap the Timer.periodic creation with a non null condition so that clicking the button multiple times has no effect

if (_timer != null) {
  _timer = new Timer.periodic(...);
}

cancel the timer and reset the countdown if you want to restart the timer on each click :

if (_timer != null) {
  _timer.cancel();
  _start = 10;
}
_timer = new Timer.periodic(...);

if you want the button to act like a play/pause button :

if (_timer != null) {
  _timer.cancel();
  _timer = null;
} else {
  _timer = new Timer.periodic(...);
}

You could also use this official async package which provides a RestartableTimer class which extends from Timer and adds the reset method.

So just call _timer.reset(); on each button click.

Finally, Codepen now supports Flutter ! So here is a live example so that everyone can play with it : https://codepen.io/Yann39/pen/oNjrVOb

I have created a Generic Timer Widget which can be used to display any kind of timer and its flexible as well.

This Widget takes following properties

secondsRemaining: duration for which timer needs to run in seconds
whenTimeExpires: what action needs to be performed if timer finished
countDownStyle: any kind of style which you want to give to timer
countDownFormatter: the way user wants to display the count down timer e.g hh mm ss string like 01 hours: 20 minutes: 45 seconds

you can provide a default formatter ( formatHHMMSS ) in case you don't want to supply it from every place.

// provide implementation for this - formatHHMMSS(duration.inSeconds); or use below one which I have provided.

import 'package:flutter/material.dart';
class CountDownTimer extends StatefulWidget {
  const CountDownTimer({
    Key key,
    int secondsRemaining,
    this.countDownTimerStyle,
    this.whenTimeExpires,
    this.countDownFormatter,
  })  : secondsRemaining = secondsRemaining,
        super(key: key);

  final int secondsRemaining;
  final Function whenTimeExpires;
  final Function countDownFormatter;
  final TextStyle countDownTimerStyle;

  State createState() => new _CountDownTimerState();
}

class _CountDownTimerState extends State<CountDownTimer>
    with TickerProviderStateMixin {
  AnimationController _controller;
  Duration duration;

  String get timerDisplayString {
    Duration duration = _controller.duration * _controller.value;
    return widget.countDownFormatter != null
        ? widget.countDownFormatter(duration.inSeconds)
        : formatHHMMSS(duration.inSeconds);
      // In case user doesn't provide formatter use the default one
     // for that create a method which will be called formatHHMMSS or whatever you like
  }

  @override
  void initState() {
    super.initState();
    duration = new Duration(seconds: widget.secondsRemaining);
    _controller = new AnimationController(
      vsync: this,
      duration: duration,
    );
    _controller.reverse(from: widget.secondsRemaining.toDouble());
    _controller.addStatusListener((status) {
      if (status == AnimationStatus.completed || status == AnimationStatus.dismissed) {
        widget.whenTimeExpires();
      }
    });
  }

  @override
  void didUpdateWidget(CountDownTimer oldWidget) {
    if (widget.secondsRemaining != oldWidget.secondsRemaining) {
      setState(() {
        duration = new Duration(seconds: widget.secondsRemaining);
        _controller.dispose();
        _controller = new AnimationController(
          vsync: this,
          duration: duration,
        );
        _controller.reverse(from: widget.secondsRemaining.toDouble());
        _controller.addStatusListener((status) {
          if (status == AnimationStatus.completed) {
            widget.whenTimeExpires();
          } else if (status == AnimationStatus.dismissed) {
            print("Animation Complete");
          }
        });
      });
    }
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return new Center(
        child: AnimatedBuilder(
            animation: _controller,
            builder: (_, Widget child) {
              return Text(
                timerDisplayString,
                style: widget.countDownTimerStyle,
              );
            }));
  }
}

Usage:

 Container(
       width: 60.0,
       padding: EdgeInsets.only(top: 3.0, right: 4.0),
         child: CountDownTimer(
           secondsRemaining: 30,
           whenTimeExpires: () {
              setState(() {
                hasTimerStopped = true;
              });
            },
            countDownTimerStyle: TextStyle(
                color: Color(0XFFf5a623),
                fontSize: 17.0,
                height: 1.2,
            ),
          ),
        )

example for formatHHMMSS:

String formatHHMMSS(int seconds) {
  int hours = (seconds / 3600).truncate();
  seconds = (seconds % 3600).truncate();
  int minutes = (seconds / 60).truncate();

  String hoursStr = (hours).toString().padLeft(2, '0');
  String minutesStr = (minutes).toString().padLeft(2, '0');
  String secondsStr = (seconds % 60).toString().padLeft(2, '0');

  if (hours == 0) {
    return "$minutesStr:$secondsStr";
  }

  return "$hoursStr:$minutesStr:$secondsStr";
}

Null Safe Version of the Above Code

import 'package:flutter/material.dart';

class CountDownTimer extends StatefulWidget {
  const CountDownTimer({
    Key? key,
    required this.secondsRemaining,
    required this.whenTimeExpires,
    this.countDownFormatter,
    this.countDownTimerStyle,
  }) : super(key: key);

  final int secondsRemaining;
  final VoidCallback whenTimeExpires;
  final TextStyle? countDownTimerStyle;
  final Function(int seconds)? countDownFormatter;

  @override
  State createState() => _CountDownTimerState();
}

class _CountDownTimerState extends State<CountDownTimer>
    with TickerProviderStateMixin {
  late final AnimationController _controller;
  late final Duration duration;

  String get timerDisplayString {
    final duration = _controller.duration! * _controller.value;
    if (widget.countDownFormatter != null) {
      return widget.countDownFormatter!(duration.inSeconds) as String;
    } else {
      return formatHHMMSS(duration.inSeconds);
    }
  }

  String formatHHMMSS(int seconds) {
    final hours = (seconds / 3600).truncate();
    seconds = (seconds % 3600).truncate();
    final minutes = (seconds / 60).truncate();

    final hoursStr = (hours).toString().padLeft(2, '0');
    final minutesStr = (minutes).toString().padLeft(2, '0');
    final secondsStr = (seconds % 60).toString().padLeft(2, '0');

    if (hours == 0) {
      return '$minutesStr:$secondsStr';
    }

    return '$hoursStr:$minutesStr:$secondsStr';
  }

  @override
  void initState() {
    super.initState();
    duration = Duration(seconds: widget.secondsRemaining);
    _controller = AnimationController(
      vsync: this,
      duration: duration,
    );
    _controller
      ..reverse(from: widget.secondsRemaining.toDouble())
      ..addStatusListener((status) {
        if (status == AnimationStatus.completed ||
            status == AnimationStatus.dismissed) {
          widget.whenTimeExpires();
        }
      });
  }

  @override
  void didUpdateWidget(CountDownTimer oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (widget.secondsRemaining != oldWidget.secondsRemaining) {
      setState(() {
        duration = Duration(seconds: widget.secondsRemaining);
        _controller.dispose();
        _controller = AnimationController(
          vsync: this,
          duration: duration,
        );
        _controller
          ..reverse(from: widget.secondsRemaining.toDouble())
          ..addStatusListener((status) {
            if (status == AnimationStatus.completed) {
              widget.whenTimeExpires();
            }
          });
      });
    }
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Center(
      child: AnimatedBuilder(
        animation: _controller,
        builder: (_, Widget? child) {
          return Text(
            timerDisplayString,
            style: widget.countDownTimerStyle,
          );
        },
      ),
    );
  }
}

Little late to the party but why don't you guys try animation.No I am not telling you to manage animation controllers and disposing them off and all that stuff, there's a built-in widget for that called TweenAnimationBuilder. You can animate between values of any type, here's an example with a Duration class

TweenAnimationBuilder<Duration>(
  duration: Duration(minutes: 3),
  tween: Tween(begin: Duration(minutes: 3), end: Duration.zero),
  onEnd: () {
    print('Timer ended');
  },
  builder: (BuildContext context, Duration value, Widget? child) {
    final minutes = value.inMinutes;
    final seconds = value.inSeconds % 60;
    return Padding(
      padding: const EdgeInsets.symmetric(vertical: 5),
      child: Text('$minutes:$seconds',
               textAlign: TextAlign.center,
               style: TextStyle(
               color: Colors.black,
               fontWeight: FontWeight.bold,
               fontSize: 30)));
    }),

and You also get onEnd call back which notifies you when the animation completes;

here's the output

Flutter Countdown Timer

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