Flutter - Using Timer and .cancel() function-CodePudding

*** UPDATE ***

I have a problem. When I use a Timer in Flutter and cancel() it afterwards, but as soon the cancel method is triggered, nothing happens.

var counter = 0;

Timer.periodic(const Duration(milliseconds: 50), (timer) {

developer.log('Actual counter '   counter.toString());
counter  ;
 
if (counter == 5) {
   developer.log('TIMER DONE');
    timer.cancel();
}

});

developer.log('This comes afterwards');

Expected out put:

Actual counter 0
Actual counter 1
Actual counter 2
Actual counter 3
Actual counter 4
TIMER DONE
This comes afterwards

The Output:

Actual counter 0
Actual counter 1
Actual counter 2
Actual counter 3
Actual counter 4
TIMER DONE

normally I should see a message 'this is afterwards' in the console, but it seems that with the cancel the complete method will be canceled.

Many thanks in advance.

CodePudding user response：

Update: perform operation end of timer.

You need to add logic inside if condition to perform operation.

if (counter == firmwareList.length) {
    timer.cancel();
    developer.log('This comes afterwards'); //here
      }
});

Here is an widget example

class TimerF extends StatefulWidget {
  const TimerF({super.key});

  @override
  State<TimerF> createState() => _TimerFState();
}

class _TimerFState extends State<TimerF> {
  var counter = 0;

  Timer? timer;

  bool isTimerActive = true;

  @override
  void initState() {
    super.initState();
    timer = Timer.periodic(const Duration(seconds: 1), (timer) {
      print('Still timer');

      if (counter == 5) {
        timer.cancel();
        isTimerActive = false;
      }
      counter  ;
      setState(() {});
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        children: [
          Text("current value ${counter}"),
          if (timer?.isActive == false) Text("Timer isnt active"),
          if (isTimerActive == false) Text("Timer isnt active $isTimerActive"),
        ],
      ),
    );
  }
}

I can't see any increment on counter on current snippet. that's why counter remains 0 and doesnt meet the condition to cancel the timer.

Perhaps it will be

var counter = 0;
Timer.periodic(const Duration(milliseconds: 50), (timer) {
  print('Still timer');

  if (counter == 5) {
    timer.cancel();
  }
  counter  ; //increment the value
  print('this is afterwards');
});

CodePudding user response：

Here is a fully working example using a Timer

Timer? timer;

startTimer() {
  var counter = 0;
  timer = Timer.periodic(const Duration(milliseconds: 50), (timer) {
    counter  = 1;
    print('Actual step $counter');
    if(counter==5) {
      cancelTimer();
    }
  });
}

cancelTimer() {
  timer?.cancel();
  print('this is afterwards');
  //do something here
}

When you startTimer(), here is the output

Actual step 1
Actual step 2
Actual step 3
Actual step 4
Actual step 5
this is afterwards