Dealing with FirebaseUI sign-in and offline Firestore data?

Question

I am having difficulty figuring out how user authentication/sign-in via FirebaseUI works in relation to the offline persistence of data from a Firestore database in Android.

I understand a user must be signed in in order to retrieve their documents from the database but what happens when the user is offline? How do I set up the flow of user and data checks in my app before displaying the user's list of documents, if any?

Please correct me if my understanding of the documentation (FirebaseUI and Firestore offline data) below is wrong.

So there are I think basically 3 pages a user would see:

1. A sign-up/sign-in page
2. An empty page when the user has no data in the database
3. A list of their documents

The first sign-up/sign-in page should be displayed for first time users and signed out users (whether the user has signed-out themselves or their sign-in token has expired). This is where FirebaseUI comes to the rescue. Can I check for both cases with just the getCurrentUser method? What does this method return when the user is offline? Have I missed this somewhere in the documentation on managing users?

The second empty page should be displayed for signed in users who don't have any data in the database (whether because they have just signed in for the first time or they have deleted all of their data). Do I use a get call to check for data? What does it return when there is no data or what listener do I have to use? Have I missed this somewhere in the documentation on getting data?

The third list page should be displayed for signed in users who have existing data or who have just created data/documents. This can be obtained with a query on a collection via a get call on that collection.

Finally, would you tie all this together from within one activity/fragment in the following way and order in onCreate/onCreateView?

First - Check for first time and signed out users: If yes then display (inflate) the first page (i.e. launch the FirebaseUI sign in intent activity). What happens after the user has signed up/signed in? Is the user brought back to the originating activity/fragment? How do I handle this?

Second - Check for data in the database: If there is no data then display an 'empty' page. If there is data then display the list of documents instead. It seems this can be handled by switching visibility between say a TextView with the text "Empty" and the RecyclerView in the same layout (see this SO post).

Please help!

Answer 1

Can I check for both cases with just the getCurrentUser method? What does this method return when the user is offline?

When calling getCurrentUser() method on a FirebaseAuth object it returns an object of type FirebaseUser if the authentication process is successful.

FirebaseUser firebaseUser = firebaseAuth.getCurrentUser();

But before that you need to instantiate the firebaseAuth object by calling the static FirebaseAuth.getInstance() method like this:

FirebaseAuth firebaseAuth = FirebaseAuth.getInstance();

So if the authentication process is successful and you are getting offline, it doesn't matter, calling getCurrentUser() will always return the FirebaseUser object.

Do I use a get call to check for data?

Yes, you should use a get() call and first time check if (task.isSuccessful()) and second if the data exist at a particular location.

What does it return when there is no data or what listener do I have to use?

It will return an empty DocumentSnapshot object. So first you'll need to use a get() and use the addOnCompleteListener().

This can be obtained with a query on a collection via a get call on that collection.

Yes that's correct.

Finally, would you tie all this together from within one activity/fragment in the following way and order in onCreate/onCreateView?

Yes, you can tie all this together from within one activity/fragment.

What happens after the user has signed up/signed in? Is the user brought back to the originating activity/fragment? How do I handle this?

If the user signs out, you should redirect the user to the LoginActivity. I have exaplained in one of my tutorials step by step, the entire authentication process using Google and Firebase.

Check for data in the database: If there is no data then display an 'empty' page.

This is a recommended way in which you can retrieve data from a Cloud Firestore database and display it in a RecyclerView using FirestoreRecyclerAdapter. So in such case you can override the onDataChanged() like this:

@Override
public void onDataChanged() {
    if (getItemCount() == 0) {
        recyclerView.setVisibility(View.GONE);
        emptyView.setVisibility(View.VISIBLE);
    } else {
        recyclerView.setVisibility(View.VISIBLE);
        emptyView.setVisibility(View.GONE);
    }
}