Run Function / Get Data when loading new screen in Flutter - flutter

Question

I am trying to run a function that gets data via an API call that needs to initialize before / while loading the screen. I have tried using a future builder, and other methods, and perhaps i am not implementing this correctly but i cannot figure out how to do this. I have also called an async method that uses setState within my initstate method which works, but it initially loads and returns an error and what I assume is that after the state rebuilds it displays correctly.Ideally this should get the data before actually loading the screen to avoid errors.
Code for my main function in the main.dart file
void main() async {
WidgetsFlutterBinding.ensureInitialized();
SystemChrome.setPreferredOrientations(
[DeviceOrientation.portraitUp, DeviceOrientation.portraitDown]
);
final Future<SharedPreferences> _prefs = SharedPreferences.getInstance();
final SharedPreferences prefs = await _prefs;
late String initialRoute;
var accessToken = prefs.getString('access_token');
var refreshToken = prefs.getString('refresh_token');
if (accessToken != null && refreshToken != null) {
var response = await sessionRefresh(accessToken);
if (response.statusCode == 200) {
initialRoute = kDashboardID;
}
else if (response.statusCode == 401) {
var refreshResponse = await tokenRefresh(refreshToken);
if (refreshResponse.statusCode == 200) {
prefs.setString('access_token', jsonDecode(refreshResponse.body)["access_token"]);
initialRoute = kDashboardID;
}
else {
initialRoute = kLoginScreenID;
}
}
}
else {
initialRoute = kLoginScreenID;
}
runApp(MyApp(initialRoute: initialRoute,));
}
class MyApp extends StatelessWidget {
//const MyApp({Key? key}) : super(key: key);
final Future<SharedPreferences> _prefs = SharedPreferences.getInstance();
String initialRoute;
MyApp({required this.initialRoute});
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return ChangeNotifierProvider(
create: (context) => UserData(),
child: MaterialApp(
debugShowCheckedModeBanner: false,
routes: {
kLaunchScreenID: (context) => LaunchScreen(),
kLoginScreenID: (context) => LoginScreen(),
kUserRegistrationID: (context) => UserRegistration(),
kAccountVerificationID: (context) => OTPVerification(),
kDashboardID: (context) => Dashboard(),
kAccountsID: (context) => Accounts(),
},
initialRoute: initialRoute,
),
);
}
}
The ideal result would be when the initialRoute equals "kDashboardID" (user dashboard) i need to run a function that gets data so that the data can be used to populate certain widgets (text widgets, etc.) on the dashboard screen.
Not sure how to best to accomplish this.