flutter ,dart 和当前时间对比倒计时

void _timeFunc(time){
    var _newDate = DateTime.now();
    const period = const Duration(seconds: 1);
    print(time);
    var _diffDate = DateTime.parse(time.toString());
    _timerIndex = Timer.periodic(period, (timer) {
      //到时回调
      _diffDate =  _diffDate.subtract(Duration(seconds: 1));
      // count++;
      if (_diffDate.difference(_newDate).inSeconds <= 0) {
        //取消定时器，避免无限回调
        timer.cancel();
        timer = null;
      }
      // print();
      var _surplus = _diffDate.difference(_newDate);
      int _day = (_surplus.inSeconds ~/ 3600) ~/ 24;
      int hour = (_surplus.inSeconds ~/ 3600) % 24;
      int minute = _surplus.inSeconds % 3600 ~/ 60;
      int second = _surplus.inSeconds % 60;
    // formatTime(hour) + ":" + formatTime(minute) + ":" + formatTime(second);
      setState(() {
        _day1 = _day.toString()??'0';
        _hour1 = hour.toString()??'0';
        _minute1 = minute.toString()??'0';
        _second1 = second.toString()??'0';
        // _text = _diffDate.weekday.toString()+'  ' +_diffDate.hour.toString()+':' + _diffDate.minute.toString() +':'+ _diffDate.second.toString();
      });
      // debugPrint(_text);
    });
  }