How to set text values to change automatically in flutter? - flutter

Question

I'm new to flutter and developing an app in which vehicle speed is shown in the floating action button in Scaffold. But I want it to change according to speed automatically so that it doesn't need to refresh/restart manually every time.
Here's my code.
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:geolocator/geolocator.dart';
class HomePage extends StatefulWidget {
#override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
double speedInMps;
double speedInKph;
var geolocator = Geolocator();
var locationOptions = LocationOptions(accuracy: LocationAccuracy.high,
distanceFilter: 10);
Future<void> getVehicleSpeed()async{
try{
geolocator.getPositionStream((locationOptions)).listen((position) async
{
speedInMps = await position.speed;
speedInKph = speedInMps * 1.609344;
print(speedInKph.round());
});
}catch(e){
print(e);
}
}
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold( floatingActionButton: FloatingActionButton(
onPressed: () {getVehicleSpeed();
},
child: Text(speedInKph.round().toString() +'Km/h'),//Need Improvments
Here
backgroundColor: Colors.green,
),
appBar: AppBar(
title: Text('speed'),
centerTitle: true,
),
body: Center(
child: FlatButton(
onPressed: getVehicleSpeed,
child: Text(
speedInKph.toString(),
style: TextStyle(fontSize: 16.0),
),
color: Color(0xffdd4b39),
textColor: Colors.white,
padding: const EdgeInsets.all(20.0),
),
),
)
);
}
}
I have to hot reload/restart to get updated speed, but I want it to refresh speed automatically.

Answer 1

You need to listen location only once. So put in initState which called when widget is initialized.
#override
void initState() {
super.initState();
getVehicleSpeed();
}
And than call setState method when data is change. It will rebuild the widget.
Future<void> getVehicleSpeed() async {
try {
geolocator.getPositionStream((locationOptions)).listen((position) async {
speedInMps = position.speed;
setState(() {
speedInKph = speedInMps * 1.609344;
});
print(speedInKph.round());
});
} catch (e) {
print(e);
}
}