Firebase Realtime Database and Flutter - Snapshot has no data - flutter

Question

I try to implement the Firebase Realtime Database in Flutter and I want to display updated values in realtime. I try to achieve this with a StreamBuilder.
StreamBuilder Code
StreamBuilder(
stream: GuestbooksDatabase().getAllGuestbooksSync().asStream(),
builder: (context, snapshot) {
if (!snapshot.hasData || !snapshot.data.length) {
return CircularProgressIndicator();
} else {
return ListView.builder(
shrinkWrap: true,
itemCount: snapshot.data.length,
itemBuilder: (context, index) {
return Text(snapshot.data[index].title);
});
}
}),
The stream function
Future<List<Guestbook>> getAllGuestbooksSync() async {
List<Guestbook> guestbooks = [];
databaseRef.onValue.listen((event) async {
var dataSnapshot = event.snapshot;
if (dataSnapshot.value != null) {
dataSnapshot.value.forEach((key, value) async {
Guestbook guestbook = await Guestbook.fromJson(value);
guestbook.setId(key);
guestbooks.add(guestbook);
});
await Future.delayed(Duration.zero);
print(guestbooks); // Result: All Instances of Guestbook
return guestbooks;
}
});
}
I only see the CircularProgressIndicator() what means that the snapshot has no data.
What's the issue there?

Answer 1

You can use StreamController for this.
Create a new controller -
final StreamController streamController = StreamController<List>.broadcast();
Convert Future<List> to void type for your getAllGuestbooksSync() function and return nothing.
It can and will be called in initState() -
void getAllGuestbooksSync() {
List<Guestbook> guestbooks = [];
databaseRef.onValue.listen((event) async {
var dataSnapshot = event.snapshot;
if (dataSnapshot.value != null) {
dataSnapshot.value.forEach((key, value) async {
Guestbook guestbook = await Guestbook.fromJson(value);
guestbook.setId(key);
guestbooks.add(guestbook);
});
print(guestbooks); // Result: All Instances of Guestbook
streamController.add(guestbooks); // Adding list to the stream
}
});
}
In your StreamBuilder use -
stream: streamController.stream,