(Android App) Is there a way to retrieve data from a Firebase database while inside the SnapshotParser part of the FirebaseRecyclerOptions query?

So, as the title says, I am looking to retrieve data from a Firebase database before constructing an object in FirebaseRecyclerOptions to be used in a FirebaseRecyclerAdapter. Basically, what I am trying to do is make a friends list in an app I'm working on. This what the database looks like:

Friends:
  uid1:
    id: friendID
  uid2:
    id: friendID

Users:
  uid1:
    name: name
    status: status
    image: profileImageUrl
  uid2:
    name: name
    status: status
    image: profileImageUrl

I've got code that currently looks like this:

FirebaseRecyclerOptions<Users> options = new FirebaseRecyclerOptions.Builder<Users>().setQuery(usersDatabase, new SnapshotParser<Users>() {
        @NonNull
        @Override
        public Users parseSnapshot(@NonNull DataSnapshot snapshot) {
            System.out.println(snapshot);
            rootRef.child("Users").child(snapshot.getValue().toString()).addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    System.out.println(dataSnapshot);
                    name = dataSnapshot.child("name").getValue().toString();
                    status = dataSnapshot.child("status").getValue().toString();
                    image = dataSnapshot.child("image").getValue().toString();
                    return;
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });
            System.out.println(snapshot);
            return new Users(name, image, status);
        }
    }).build();

The problem is that the ValueEventListener I add does not trigger until after the new Users instance is returned. Should I be adding the ValueEventListener to the same DatabaseReference (userDatabase) as the FirebaseRecyclerOptions query?

What you're trying to do isn't really possible with FirebaseUI. The snapshot parser needs to return a User object immediately, or synchronously. You can't perform an asynchronous database query (which does not complete immediately, or even guaranteed to complete at all) in order to provide that value.

If you need to perform multiple queries in order to populate your views, you won't be able to use FirebaseUI effectively. You should probably consider doing all your lookups ahead of time, or write a special adapter that allows view contents to be populated asynchronously as the results become available. This will end up being a lot of code to do correctly.

It perhaps seems a little redundant to be answering my own question, but this is mostly for anyone else that has trouble with this. Following @Doug Stevenson's suggestion, I started trying to make my own custom recycler adapters and options class. However, I realized that the queries for the options could be modified. So basically, the solution is this:

Query query = database.collection("Users");
@Override
protected void onStart() {
super.onStart();
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DocumentReference ref = FirebaseFirestore.getInstance().collection("Users").document(uid);
ref.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
@Override
public void onComplete(@NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()){
DocumentSnapshot document = task.getResult();
if (document.exists()) {
friends = (ArrayList<String>) document.get("friends");
if (friends.size() > 0) {
FirestoreRecyclerOptions<Users> options = new FirestoreRecyclerOptions.Builder<Users>().setQuery(query.whereIn("user_id", friends), Users.class).build();
FirestoreRecyclerAdapter<Users, UsersViewHolder> adapter = new FirestoreRecyclerAdapter<Users, UsersViewHolder>(options) {
@Override
public UsersViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext())
.inflate(R.layout.single_user_layout, parent, false);
return new UsersViewHolder(view);
}
@Override
protected void onBindViewHolder(@NonNull UsersViewHolder usersViewHolder, int i, @NonNull Users users) {
if (users != null) {
usersViewHolder.setName(users.name);
usersViewHolder.setStatus(users.status);
usersViewHolder.setImg(users.image);
final String userID = getSnapshots().getSnapshot(i).getId();
usersViewHolder.mView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent profilePage = new Intent(FriendsList.this, ProfileActivity.class);
profilePage.putExtra("userID", userID);
startActivity(profilePage);
}
});
}
}
};
usersListPage.setAdapter(adapter);
adapter.startListening();
}
}
}
}
});
}

In the setQuery method, rather than using the collection reference as the query, I created a query object from it, and then modified the query query.whereIn(), which allows you to check to see if the field of a document contains the given object or one of the objects in a list.

My code here is very much a mess, I know.