CODEWITHSUNDEEP
flutterdartasync-await
Nikash Deka
Nikash Deka

Reputation: 427

Implementing async / await in Dart/Flutter

  1. Why the build method is showing 'NULL' at Restart, but update the Latitude value on hot-reload?

  2. Is it possible to load the Text('Lat: $latitude') as initState() itself?

class _LoadingScreenState extends State<LoadingScreen> {
  double latitude;
  double longitude;

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

  void getLocation() async {
    Location location = Location();

    await location.getCurrentLocation();

    latitude = location.latitude;
    longitude = location.longitude;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(child: Text('Lat: $latitude')),
    );
  }
}

Upvotes: 0

Views: 219

Answers (3)

Zah
Zah

Reputation: 116

as with the answer above, the getLocation is async meaning it will finish in future, on restart you get the current latitude which is null then as it didn't get the value yet, when hot reloading you get to show the value then which is already finished, you can use setState in stateful class as above, or you can use futurebuilder to show the value when available.

Upvotes: 0

Robert Sandberg
Robert Sandberg

Reputation: 8597

latitude havn't had time to be assigned with a value when the build method is constructing the widget.

Wrap the assignment of latitude and longitude with the setState method to notify the framework that a new build should take place. That way the latitude value will be updated as soon as it is available.

setState(() {
 latitude = location.latitude;
 longitude = location.longitude;
});

A tip is to display something else instead of the latitude value while waiting for it to be assigned. This could e.g. be a CircularProgressIndicator.

Upvotes: 1

Kise
Kise

Reputation: 2905

That's because you haven't called the setState method when you changed your data, so the widget did not rebuild itself.

It should be like this:

void getLocation() async {
    Location location = Location();

    await location.getCurrentLocation();

    setState(() {
      latitude = location.latitude;
      longitude = location.longitude;
    });
  }

Upvotes: 1

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