How to implement a simple Countdown timer constructor into an app in flutter?

Question

I am a beginner in flutter and I wanted to implement a simple CountDown Time (that counts in minutes and seconds) in my quiz app.

I tried to implement the CountdownTimer constructor I found in the official Flutter doc site, but I couldn't apply the constructor into real code in my application. I was able to copy the code provided by @Yann39 at (Flutter Countdown Timer) which worked. But I would like to learn how to implement the constructor myself.

Timer _timer;
int _start = 10;

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

@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")
        ],
      ));
}

CountdownTimer constructor

CountdownTimer(
Duration duration,
Duration increment, {
Stopwatch stopwatch
})

I basically want to know how to implement the CountDown timer constructor to create my code. I believe knowing this will also help me implement and interpret other constructors I encounter.

Answer 1

CountdownTimer is used when you have to do some work every time for specific amount of time. Here is an example to show you that.

CountdownTimer countdownTimer = CountdownTimer(
  Duration(seconds: 5),
  Duration(seconds: 1),
);
countdownTimer.listen((timer) {
  // this code runs every second for 5 seconds
});