6-16 倒數計時做某件事

class _ApplyDetailState extends State<ApplyDetail> {
  bool _show = true;
  Timer _timer;
  int count=3;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _timer = Timer.periodic(Duration(seconds: 1), (Timer timer) {
      if(count==0) {
        _timer.cancel();
        _show = false;
        setState(() {
          count;
        });
        return;
      }
      count--;
    });
  }
  ...略...
}