How update Widget when time is 23:59:59? - flutter

Question

After doing an event..I want to show up my Text widget and change that widget when the time is at 23:59:59... so far I have done this code
DateFormat("HH:mm:ss").format(DateTime.now()) =="23:59:59"
? Text("After")
: Text("Before")
but the problem is... whenever I close my app and then re-open app... the widget doesn't change from Text("Before") to Text("After") although the time is already at 23:59:59... the widget only change after I am doing an event click and when app is still opened... is there a way to solve that problem without any additional event?

Answer 1

You have your Texts in build method. This method works only on widget's update, for example, if state changes (that's why widget updates when you do an event click, I think your widget rebuilds after click). But widget doesn't know anything about DateTime.now(). So you should put DateTime.now to state and update it once in second.
import 'package:flutter/material.dart';
import 'package:intl/intl.dart';
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: SafeArea(
child: Padding(
padding: EdgeInsets.all(16),
child: BeforeAfter(),
),
),
),
);
}
}
class BeforeAfter extends StatefulWidget {
#override
_BeforeAfterState createState() => _BeforeAfterState();
}
class _BeforeAfterState extends State<BeforeAfter> {
String time = DateFormat("HH:mm:ss").format(DateTime.now()); // our time which we will update
#override
void initState() {
super.initState();
updateTime();
}
void updateTime() {
Future.delayed(Duration(seconds: 1), () {
updateTime();
setState(() {
time = DateFormat("HH:mm:ss").format(DateTime.now()); // update time
});
});
}
#override
Widget build(BuildContext context) {
return Column(children: <Widget>[
time == "12:13:00" ? Text("After") : Text("Before"),
Text(time)
]); // compare time with some value
}
}
void main() {
runApp(MyApp());
}
Gif how it works