How to access widget in an initializer in google maps flutter - flutter

Question

I am passing select latitude and longitude from google maps to my flutter app's another screen where I am calculating the distance between 2 locations.
I've got the values coming fine but there's this widget can't be accessed in an initializer issue coming.
I'm using google maps and I've to pass the widget.lat widget.long values to the userLocation marker.
I'm using this tutorial's code by the way
Get distance between locations
Here's my code
class CalculateDistance extends StatefulWidget {
const CalculateDistance({super.key, required this.lang, required this.lat});
final double lang;
final double lat;
#override
// ignore: library_private_types_in_public_api
_CalculateDistanceState createState() => _CalculateDistanceState();
}
class _CalculateDistanceState extends State<CalculateDistance> {
GoogleMapController? mapController; //contrller for Google map
PolylinePoints polylinePoints = PolylinePoints();
String googleAPiKey = "YOUR_API_KEY";
Set<Marker> markers = {}; //markers for google map
Map<PolylineId, Polyline> polylines = {}; //polylines to show direction
LatLng storeLocation =
const LatLng(-30.600164342582726, 23.508854043469647); // Store location
// This is where I can't use the passed values
LatLng userLocation = LatLng(widget.lat, widget.lang); // User location
double distance = 0.0;
#override
void initState() {
markers.add(Marker(
//add start location marker
markerId: MarkerId(storeLocation.toString()),
position: storeLocation, //position of marker
infoWindow: const InfoWindow(
//popup info
title: 'Store Location',
snippet: 'Store Marker',
),
icon: BitmapDescriptor.defaultMarker, //Icon for Marker
));
markers.add(Marker(
//add distination location marker
markerId: MarkerId(userLocation.toString()),
position: userLocation, //position of marker
infoWindow: const InfoWindow(
//popup info
title: 'User Location',
snippet: 'User Marker',
),
icon: BitmapDescriptor.defaultMarker, //Icon for Marker
));
getDirections(); //fetch direction polylines from Google API
super.initState();
}
getDirections() async {
List<LatLng> polylineCoordinates = [];
PolylineResult result = await polylinePoints.getRouteBetweenCoordinates(
googleAPiKey,
PointLatLng(storeLocation.latitude, storeLocation.longitude),
PointLatLng(userLocation.latitude, userLocation.longitude),
travelMode: TravelMode.driving,
);
if (result.points.isNotEmpty) {
for (var point in result.points) {
polylineCoordinates.add(LatLng(point.latitude, point.longitude));
}
} else {
print(result.errorMessage);
}
//polulineCoordinates is the List of longitute and latidtude.
double totalDistance = 0;
for (var i = 0; i < polylineCoordinates.length - 1; i++) {
totalDistance += calculateDistance(
polylineCoordinates[i].latitude,
polylineCoordinates[i].longitude,
polylineCoordinates[i + 1].latitude,
polylineCoordinates[i + 1].longitude);
}
print(totalDistance);
setState(() {
distance = totalDistance;
});
//add to the list of poly line coordinates
addPolyLine(polylineCoordinates);
}
addPolyLine(List<LatLng> polylineCoordinates) {
PolylineId id = const PolylineId("poly");
Polyline polyline = Polyline(
polylineId: id,
color: Colors.deepPurpleAccent,
points: polylineCoordinates,
width: 8,
);
polylines[id] = polyline;
setState(() {});
}
double calculateDistance(lat1, lon1, lat2, lon2) {
var p = 0.017453292519943295;
var a = 0.5 -
cos((lat2 - lat1) * p) / 2 +
cos(lat1 * p) * cos(lat2 * p) * (1 - cos((lon2 - lon1) * p)) / 2;
return 12742 * asin(sqrt(a));
}
// Scaffold ahead

Answer 1

Declare this LatLng with late keyword as a member of _CalculateDistanceState class:
class _CalculateDistanceState extends State<CalculateDistance> {
late LatLng _userLocation;
(...)
}
Then in the initState you will have access to the widget:
void initState() {
super.initState();
_userLocation = LatLng(widget.lat, widget.lang);
(...)
}