How to use a Future in a StreamBuilder in Flutter [duplicate] - string

Question

This question already has answers here:
What is a Future and how do I use it?
(6 answers)
Closed 2 years ago.
I'm trying to build my first mobile application with flutter and firebase.
Error:
The argument type 'Future Function()' can't be assigned to the parameter type 'String'
class ShowUserData extends StatefulWidget {
#override
_ShowUserDataState createState() => _ShowUserDataState();
}
class _ShowUserDataState extends State<ShowUserData> {
final email = () {
final userEmail =
FirebaseAuth.instance.currentUser().then((user) => user.email);
print('userEmail + $userEmail');
return userEmail;
};
#override
Widget build(BuildContext context) {
return StreamBuilder(
// stream: user.getUserData().asStream(),
stream: Firestore.instance.collection('users').document(email).snapshots(),
builder: (context, snapshot) {
if (!snapshot.hasData) {
return Text("Loading");
}
print('snapshot + $snapshot');
var userDocument = snapshot.data;
print('userDocument + $userDocument');
return Text(userDocument['firstName']);
});
}
}

Answer 1

For the first part of your code, consider something like this:
Future<String> getUserEmail() async {
final userEmail =
FirebaseUser user = await FirebaseAuth.instance.currentUser();
String userEmail = user.email;
print('userEmail + $userEmail');
return userEmail;
};
That should solve that error (hence answering your question). Although the rest of the code will still fail. You should read up on futures and async programming.
Now my suggested solution for the whole thing.
Since you have 2 different async sources that create your stream, you might want to consider creating your own Stream! (Yes, streams are powerful like that).
In sequence, you’re wanting to
await on the future: .currentUser()
use the result of that to create your firestore snapshot stream
Try something like this
class ShowUserData extends StatefulWidget {
#override
_ShowUserDataState createState() => _ShowUserDataState();
}
class _ShowUserDataState extends State<ShowUserData> {
Stream currentUserStream() async* {
FirebaseUser user = await FirebaseAuth.instance.currentUser();
String userEmail = user.email;
yield* Firestore.instance.collection('users').document(userEmail).snapshots();
};
#override
Widget build(BuildContext context) {
return StreamBuilder(
// stream: user.getUserData().asStream(),
stream: currentUserStream(),
builder: (context, snapshot) {
if (!snapshot.hasData) {
return Text("Loading");
}
print('snapshot + $snapshot');
var userDocument = snapshot.data;
print('userDocument + $userDocument');
return Text(userDocument['firstName']);
});
}
}