CODEWITHSUNDEEP
flutterfirebase-realtime-database
Vincenzo
Vincenzo

Reputation: 6368

Getting a Stream<List<Object>> from a Stream<Event> from firebase real time database Flutter

I'm very new to flutter Streams/Bloc/Provider and I'm following a tutorial to understand it. In the tutorial dough they use Firestore so they get a Stream like this:

Stream<List<Todo>> todos() {
    return todoCollection.snapshots().map((snapshot) {
      return snapshot.documents 
          .map((doc) => Todo.fromEntity(TodoEntity.fromSnapshot(doc)))
          .toList();
    });
  }

Where their snapshot is List<DocumentSnapshot>, mine from RTDB is instead an Event. I'm trying to get a Stream<List<Object>> from a RTDB node, but from the .onValue() property I get a Stream<Event>. Inside the async map() I access the snapshot Event but I don't get access to the Dart.core's map()as in the example that uses Firestore, for it's not a List. alerts() is the Stream that the bloc will be listening to but it's expecting a Stream<List<Object>> and I can't get it. How would I go to map it to a Stream<List<Object>> as I need? Thank you very much for your time and help. My code is:

// 
static UserAlert fromSnapshot(DataSnapshot snapshot) {
    return UserAlert(
        city: snapshot.value['City'],
        country: snapshot.value['Country'],
        date: snapshot.value['Date'],
        description: snapshot.value['Description'],
        id: snapshot.value['Id'],
        latitude: snapshot.value['Latitude'],
        longitude: snapshot.value['Longitude'],
        region: snapshot.value['Region'],
        timestamp: snapshot.value['Timestamp'],
        alertImageName: snapshot.value['alertImageName'],
        imageUrl: snapshot.value['imageUrl'],
        user: snapshot.value['user']);
  }


// try 1
Stream<List<UserAlert>> alerts() {
    return _databaseReference.onValue.map((snapshot) {
      // do the mapping to a Stream<List<UserAlert>>
    });
  }

 // try 2
 Stream<List<UserAlert>> alerts() {
return _databaseReference.onValue.toList(){ // Function expressions can't be named error

};

}

 // try 3
 Stream<List<UserAlert>> alerts() {
return _databaseReference.onValue.map(
    (snapshot) => UserAlert.fromSnapshot(snapshot); // wrong return type
);

}

Upvotes: 1

Views: 1783

Answers (1)

Kahou
Kahou

Reputation: 3488

Use StreamTransformer

Stream<UserAlert> alerts() {
  handleData(Event event, EventSink<UserAlert> sink) =>
      sink.add(UserAlert.fromSnapshot(event.snapshot.value));

  final transformer =
      StreamTransformer<Event, UserAlert>.fromHandlers(handleData: handleData);

  return _databaseReference.onValue.transform(transformer);
}

Upvotes: 1

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