How to periodically set state? - flutter

Question

I am trying to build a countdown app for special days for example 11 d 2 h 30 m 23s to the new year but I can't reload my state every second so it just shows me the second that I loaded the page I don't know how to dynamically reload the page.
import 'package:flutter/material.dart';
class RopSayac extends StatefulWidget {
_RopSayacState createState() => _RopSayacState();
}
class _RopSayacState extends State<RopSayac> {
var now = DateTime.now().second.toString();
String asd(){
setState(() {
now = DateTime.now().second.toString();
});
return now;
}
#override
Widget build(BuildContext context) {
return Container(
child: new Text(asd()),
);
}
}
This is what I got and it doesn't reload time. I am pretty new on the flutter.

Answer 1

As pskink and Günter mentioned, use a Timer. You can even use the periodic constructor that would fit well your scenario.
Note you don't need the asd() function. When you call setState(), the build method will be called automatically passing the new now property value.
If you want, use initState to set an initial value and, as in this example, setup the Timer.
import 'dart:async';
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(title: 'Timer Periodic Demo', home: RopSayac());
}
}
class RopSayac extends StatefulWidget {
_RopSayacState createState() => _RopSayacState();
}
class _RopSayacState extends State<RopSayac> {
String _now;
Timer _everySecond;
#override
void initState() {
super.initState();
// sets first value
_now = DateTime.now().second.toString();
// defines a timer
_everySecond = Timer.periodic(Duration(seconds: 1), (Timer t) {
setState(() {
_now = DateTime.now().second.toString();
});
});
}
#override
Widget build(BuildContext context) {
return Container(
child: Center(
child: new Text(_now),
),
);
}
}

Answer 2

This recursive method should be enough for what you want. The seconds set as 1 will keep triggering setState each second, thus refreshing your widget tree.
void _timer() {
Future.delayed(Duration(seconds: 1)).then((_) {
setState(() {
print("1 second closer to NYE!");
// Anything else you want
});
_timer();
});
}

Answer 3

There's this excellent library called timer_builder. I think it'll help you out.
Example from the pub page:
import 'package:timer_builder/timer_builder.dart';
class ClockWidget extends StatelessWidget {
#override
Widget build(BuildContext context) {
return TimerBuilder.periodic(Duration(seconds: 1), //updates every second
builder: (context) {
return Text("${DateTime.now()}");
}
);
}
}

Answer 4

Here's what I do. In my case I'm polling a webservice in _liveUpdate()
void startUpdates(AppState appState) async {
await new Future.delayed(const Duration(milliseconds: 100));
while (true) {
_liveUpdate();
appState.setState(() {});
await new Future.delayed(const Duration(seconds : 15));
}