CountdownList.dart

import 'dart:async';

import 'package:flutter/material.dart';

class CountdownList extends StatefulWidget {
  @override
  _CountdownListState createState() => _CountdownListState();
}

class _CountdownListState extends State<CountdownList> {
  String countdownText = "";

  @override
  void initState() {
    super.initState();
    startTimer();
  }

  //parsing the duration difference into D : H : M : S
  void parseCountdownToText() {
    List<String> xs = countdownText.split(":");
    int hours = int.parse(xs[0]) % 24;
    int days = int.parse(xs[0]) ~/ 24;
    int min = int.parse(xs[1]);
    int s = double.parse(xs[2]).toInt();
    countdownText = "$days\d  $hours\h  $min\m  $s\s ";
    print(countdownText);
  }

  //simple text widget to show countdown
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Text(
        "$countdownText",
        style: TextStyle(fontFamily: "Nexa", fontSize: 30),
      ),
    );
  }

  void startTimer() {
    new Timer.periodic(Duration(seconds: 1), (Timer timer) {
      setState(() {
        countdownText = DateTime.fromMillisecondsSinceEpoch(1589049000000)
            .difference(DateTime.now())
            .abs()
            .toString(); //random fixed future date
        parseCountdownToText();
      });
    });
  }
}