Flutter stopwatch running slower than expected

Question

My stopwatch is running 0.5x slower than actual time (e.g. while the real time is 1 minute, the stopwatch shows ~34 seconds).

Here is the Provider code:

class TimerState extends ChangeNotifier { 
   late String _stringTimer; 
   late Duration _duration; 
   Timer? _timer; 
  
   TimerState() { 
     _stringTimer = '00:00.00'; 
     _duration = const Duration(); 
   } 
  
   String get get => _stringTimer; 
  
   void start() { 
     _timer = Timer.periodic(const Duration(milliseconds: 1), (_) => _addTime()); 
   } 
  
   void _addTime() { 
     _duration = Duration(milliseconds: _duration.inMilliseconds + 1); 
     _formattedTimer(); 
   } 
  
   void _formattedTimer() { 
     String twoDigits(int n) => n.toString().padLeft(2, '0'); 
     final milliseconds = twoDigits((_duration.inMilliseconds.remainder(1000) / 10).floor()); 
     final seconds = twoDigits(_duration.inSeconds.remainder(60)); 
     final minutes = twoDigits(_duration.inMinutes.remainder(60)); 
     _stringTimer = '$minutes:$seconds.$milliseconds'; 
     notifyListeners(); 
   } 
 }

jamesdlin · Accepted Answer · 2022-06-09 21:06:30Z

3

Your approach adds the timer interval (1ms) on each timer event. That is a bad approach because it assumes that your timer fires exactly on every millisecond with no room for error. You also will lose time if any timer events are missed (which might happen if you ever do work that takes longer than 1ms). Error will accumulate.

Also note that 1ms is very short. Redrawing your widget every millisecond would be updating it at a rate of 1000 frames per second.

A much better approach would be to record the start time and, on each timer event, compute the difference from DateTime.now() to the start time (e.g. var elapsed = DateTime.now().difference(startTime);). That will prevent error from accumulating. Better yet, use a Stopwatch object which does that for you.

You also should pick a more reasonable timer interval; picking a rate faster than your screen's refresh rate is wasteful.

edited Jun 9, 2022 at 21:06

answered Jun 9, 2022 at 15:55

jamesdlin

91.2k14 gold badges185 silver badges225 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

chrisrn Over a year ago

Do you think 1ms can cause performance problems? because in my case it is really necessary

jamesdlin Over a year ago

@chrisrn Why is it necessary? A 1ms timer itself is not necessarily a problem, but all of the work that you currently do on each timer event is completely wasted.

jamesdlin Over a year ago

And the fact that you're dropping half of your timer events is evidence that, yes, you have a performance problem by doing too much work for a 1ms interval.

chrisrn Over a year ago

Is for accurately determine the score in a game. So, if the problem is in the process that it makes every ms, would the Stopwatch class be a solution?

jamesdlin Over a year ago

@Dani If you want to count some number of seconds, you should still use 2 DateTimes. For example, to count 10 seconds, you'd start form var now = DateTime.now(); and end at now.add(Duration(seconds: 10)).

|

Collectives™ on Stack Overflow

Flutter stopwatch running slower than expected

1 Answer 1

8 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

8 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related