Why Won't This StreamBuilder Display Data without Restarting the App? - flutter

Question

I'm trying to get a Flutter project to display a simple list of items returned from the Firebase Realtime Database. The code mostly works, but I have to restart the app each time I log out and log back in as a different user, which isn't what I'm looking for. I need the user's data to appear when they log in. I don't quite understand what all is happening here (I stumbled across a functional solution after several days of trial and error and googling), but I thought a Stream was more or less a 'live' stream of data from a particular source.
EDIT: kPAYEES_NODE is a constant stored elsewhere that resolves to 'users/uid/payees' in the RTDB:
import 'package:firebase_database/firebase_database.dart';
import 'auth_service.dart';
final DatabaseReference kUSER_NODE =
FirebaseDatabase.instance.ref('users/${AuthService.getUid()}');
final DatabaseReference kPAYEES_NODE = kUSER_NODE.child('payees');
Here's the code in question:
class DashboardPage extends StatelessWidget {
const DashboardPage({super.key});
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(...),
body: StreamBuilder(
stream: kPAYEES_NODE.onValue,
builder: (context, snapshot) {
final payees = <Payee>[];
if (!snapshot.hasData) {
return Center(child: Column(children: const [Text('No Data')]));
} else {
final payeeData =
(snapshot.data!).snapshot.value as Map<Object?, dynamic>;
payeeData.forEach((key, value) {
final dataLast = Map<String, dynamic>.from(value);
final payee = Payee(
id: dataLast['id'],
name: dataLast['name'],
note: dataLast['note'],
);
payees.add(payee);
});
return ListView.builder(
shrinkWrap: true,
itemCount: payees.length,
itemBuilder: (BuildContext context, int index) {
return ListTile(
title: Text(
payees[index].name,
style: const TextStyle(color: Colors.white),
),
subtitle: Text(
payees[index].id,
style: const TextStyle(color: Colors.white),
),
);
});
}
},
),
floatingActionButton: (...),
);
}
}

Answer 1

That's because you only get the UID of the current once in your code, here:
FirebaseDatabase.instance.ref('users/${AuthService.getUid()}')
And by the time this line runs, the AuthService.getUid() has a single value. Instead, the code needs to be reevaluated any time a users signs in or out of the app.
In an app where the user can sign in and out, the UID values are a stream like the one exposed by FirebaseAuth.instance.authStateChanges() as shown in the Firebase documentation on getting the current user. You can wrap the stream that is returned by authStateChanges() in a StreamBuilder, and then create the database reference inside of that builder, to have it respond to changes in the authentication state.