How do I calculate the sunrise and sunset in flutter? - json

Question

I would like to be able to change the text on a screen from day to night, depending on the the sun has set, or not. I found this api (https://sunrise-sunset.org/api) and more recently this package sunrise_sunset: "^1.0.3", but I am having difficulty.
This is part of a much bigger project that will be a map (google_maps) that will automatically change theme depending on the time of day(sunrise and sunset)
I know that whenever you use await, you have to make the class async, which I have done, but I am getting errors.
I have simply copied the code in the package example tab into my project
https://pub.dev/packages/sunrise_sunset#-example-tab-
I really am stuck with this, so any help would be very much appreciated.
thanks
import 'package:flutter/material.dart';
import 'package:sunrise_sunset/sunrise_sunset.dart';
void main() => runApp(JsonApiDemo());
class JsonApiDemo extends StatefulWidget {
JsonApiDemo({Key key}) : super(key: key);
#override
_JsonApiDemoState createState() => _JsonApiDemoState();
}
class _JsonApiDemoState extends State<JsonApiDemo> async {
var response = await SunriseSunset.getResults(latitude: 39.001735, longitude: -119.752744);
if (response.success) {
print('Sunrise: ${response.data.sunrise}');
print('Sunset: ${response.data.sunset}');
} else {
print(response.error);
}
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Hello World!',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: Scaffold(
appBar: AppBar(
title: Text('Hello World!'),
),
body: Center(
child: Text('Hello World!'),
),
),
);
}
}
Missing concrete implementation of State.build.
Try implementing the missing method, or make the class abstract.
A class declaration must have a body, even if it is empty.
Try adding an empty body.
Functions must have an explicit list of parameters.
Try adding a parameter list.
The await expression can only be used in an async function.
Try marking the function body with either 'async' or 'async*'.
The declaration 'build' isn't referenced.
Try removing the declaration of 'build'.

Answer 1

1 - don't mark a class as async - only functions can be async.
2 - you should call the package from an async function. The simplest way to do that is from the initState method - note initState itself is not async - so you will need another method.
3 - in that async method, store the results and call setState so that the widget is rebuilt to show them
4 - in build you need to be able to cope with the gap while the results are being fetched - use a progress indicator, etc. (I've just replaced the result with the word working).
class _JsonApiDemoState extends State<JsonApiDemo> {
DateTime sunrise;
DateTime sunset;
#override
void initState() {
super.initState();
getSunData();
}
void getSunData() async {
var response = await SunriseSunset.getResults(
latitude: 39.001735,
longitude: -119.752744,
);
if (response.success) {
var data = response.data;
setState(() {
sunrise = data.sunrise;
sunset = data.sunset;
});
print('Sunrise: $sunrise');
print('Sunset: $sunset');
} else {
print(response.error);
}
}
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Hello World!',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: Scaffold(
appBar: AppBar(
title: Text('Hello World!'),
),
body: Center(
child: Text(sunrise == null ? 'Working...' : '$sunrise-$sunset'),
),
),
);
}
}