Custom Object Retrieved from Firebase Always Has Null Attributes

Question

I'm trying to retreive a custom User object from Firebase as follows:

getUserFromDB(loggedInUserEmail);
viewModel = new ViewModelProvider(this).get(UserViewModel.class);
viewModel.sendUser(loggedInUser);

//...

public void getUserFromDB(String userEmail) {
    DocumentReference docRef = db.collection("users").document(userEmail);
    docRef.get().addOnSuccessListener(documentSnapshot -> {
        loggedInUser = documentSnapshot.toObject(User.class);

        Log.d("User Login", documentSnapshot.getId() + " => " + documentSnapshot.getData());
        Toast.makeText(MainActivity.this, "Login successful.", Toast.LENGTH_SHORT).show();
    });
}

However, the user being retreived always has null attributes. Here's a screenshot from when I was debugging.

Note: I made sure my User class has a public empty constructor and all the attributes have a getter method.

Do you have setter methods as well? – Zain Jun 17 '21 at 17:00 — Zain, Jun 17 '21 at 17:00

score 2 · Accepted Answer · edited Jun 18 '21 at 08:12

Loading the user from the database is an asynchronous operation. While the data is being loaded, the main code continues and your viewModel.sendUser(loggedInUser) executes before the data is loaded. Then the success callback is fired and sets loggedInUser, but by that time the view model has already been initialized with the wrong value.

The rule is always quite simple: any code that needs data from the database, needs to be inside the success listener (or be called from there). So something like:

public void getUserFromDB(String userEmail) {
    DocumentReference docRef = db.collection("users").document(userEmail);
    docRef.get().addOnSuccessListener(documentSnapshot -> {
        loggedInUser = documentSnapshot.toObject(User.class);
        //  Initialize ViewModelProvider here
        viewModel = new ViewModelProvider(this).get(UserViewModel.class);
        viewModel.sendUser(loggedInUser);
    });
}

Also see:

How to check a certain data already exists in firestore or not

I've been stuck on this for ages... Thank you so much! – Prescila Jun 19 '21 at 20:51 — Prescila, Jun 19 '21 at 20:51

Custom Object Retrieved from Firebase Always Has Null Attributes

1 Answers1

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