Flutter: Cannot store Firestore data to local variable (returns null) - flutter

Question

I have an issue when trying to store data from Firestore to a local variable.
class AppUser {
String _userId;
Map<String, dynamic> _userData;
Future getUserDataFromDb() async {
_userData = await dbInterface.getFinancialsFromDB(_userId);
// dbInterface.getFinancialsFromDB(_userId).then((Map<String, dynamic> data) {
// _userData = data;
// });
print(_userData); // flutter: null
}
}
_userData always returns null.
class Db {
CollectionReference financials = FirebaseFirestore.instance.collection('financials');
Future<Map<String, dynamic>> getFinancialsFromDB(userId) async {
financials.doc(userId).get().then((DocumentSnapshot documentSnapshot) {
if (documentSnapshot.exists) {
print(documentSnapshot.data()); // flutter: {'key1': 'data1', ...}
return documentSnapshot.data();
}
});
return null;
}
}
Db dbInterface = Db();
Within the "getFinancialsFromDB"-Function it prints the correct Map. So the issue isn't to retrieve the data from Firestore but to store it in the _userData variable.
The getUserDataFromDb() is called in an initState.
Any ideas what I could do to fix this issue? If you need any additional infos please let me know.
Thanks a lot, I really appreciate any help.
All the best,
Alex

Answer 1

When writing code an in async function, don't use then. Instead, use await to get the result of a Future.
Future<Map<String, dynamic>> getFinancialsFromDB(userId) async {
var documentSnapshot = await financials.doc(userId).get();
if (documentSnapshot.exists) {
return documentSnapshot.data();
}
else {
return null;
}
}