CountdownTimer constructor

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

Creates a new CountdownTimer that fires events in increments of increment, until the duration has passed.

stopwatch is for testing purposes. If you're using CountdownTimer and need to control time in a test, pass a mock or a fake. See FakeAsync and FakeStopwatch.

Implementation 

CountdownTimer(Duration duration, Duration increment, {Stopwatch stopwatch})
    : _duration = duration,
      increment = increment,
      _stopwatch = stopwatch == null ? new Stopwatch() : stopwatch,
      _controller =
          new StreamController<CountdownTimer>.broadcast(sync: true) {
  _timer = new Timer.periodic(increment, _tick);
  _stopwatch.start();
}