Firebaseui-android: FirebaseRecyclerAdapter and RecyclerView scroll position is lost on orientation change

[Calebzor]

Environment

• Android device: API 27 Emulator / Google Pixel
• Android OS version: 27 / 8.0.0
• Google Play Services version: whatever the emulator has / 11.7.45 (940-174122868)
• Firebase/Play Services SDK version: 11.4.2
• FirebaseUI version: 3.1.0

The problem:

On orientation change the recycler view using FirebaseRecyclerAdapter looses it's scroll position and is always scrolled to the top.

Steps to reproduce:

1. In the https://github.com/firebase/FirebaseUI-Android/blob/master/app/src/main/java/com/firebase/uidemo/database/realtime/RealtimeDbChatActivity.java#L110 comment out:

        // Scroll to bottom on new messages
        adapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
            @Override
            public void onItemRangeInserted(int positionStart, int itemCount) {
                mRecyclerView.smoothScrollToPosition(adapter.getItemCount());
            }
        });

so it does not get execute. This is needed so there is no extra logic forcing a scroll position.

1. Build the demo app
2. Add a bunch of chat messages, a lot so you get a scrolling regardless of orientation
3. Scroll neither to the top nor the bottom
4. Rotate the emulator

Observed Results:

• After rotation the recycler view lost it's scroll position and is scrolled to the top.

Expected Results:

• The recycler view should keep it's scroll position on orientation change.

[SUPERCILEX]

@Calebzor This is expected behavior because FirebaseUI doesn't have a stable data source—that is, we have to resubscribe and regenerate the entire list on each screen rotation. However, using Android Architecture Components, you can fairly easily keep a FirestoreArray instance to keep alive across config changes.

I have a project with (probably) too much infrastructure to make things easily understandable, but it will hopefully help you understand my explanation. Here's a high level overview:

• Create a ViewHolder that can take in ObservableSnapshotArrays and provides an exposed api to get them back. This will be used across your app.
• In the ViewHolder, add a no-op subscription to the array so that it starts a connection to the database
• In your Activity/Fragment, pass in the snapshot array to the adapter and a LifecycleOwner
• Now you have a stable data source that will survive across config changes. To save the user's battery, make sure to check out ListenerRegistrationLifecycleOwner
• In your ViewHolder's onCleared() method, kill the snapshot array
• Voila! 😄

@samtstern Since the above is a bit much, do you think we should provide that functionality out of the box? I'd have to spend way more time thinking about the APIs, but I definitely think it's possible without too much messiness.

[SUPERCILEX]

Oh lol, as I was looking through my code to explain this I found a bug. Thanks for helping me find a bug?
😆 Anyway, I've updated the commit references to include the bugfix.

[ncherian]

I also experience a similar issue. The scroll position is not retained when returning back from next screen and the screen goes back to first item on recycler view list. How to solve it?

[SUPERCILEX]

See my answer above.

[ncherian]

@SUPERCILEX I solved my problem with a simpler solution. I just called adapter.startListening(); in onViewCreated() instead of onStart and called adapter.stopListening(); in onDestroyView() instead of onStop()
That prevented the entire list from regenerating while coming back from next activity and thus retained the scroll position where it was previously.

[samtstern]

Thanks everyone for commenting! This seems like it's working as intended from the FBUI perspective, so closing the issue.

[SUPERCILEX]

@ncherian that works for the simple case but doesn't address screen rotations. When you get to that point in development, feel free to come back to this comment. 😄

@samtstern what do you think of https://github.com/firebase/FirebaseUI-Android/issues/998#issuecomment-342333313?

[ashfaaaa]

@SUPERCILEX @ncherian hi im new to android development.. how can i get it done? can you give me detailed instruction on how can i get it done it?

[dmkdfc]

@ncherian how did u do it ? please can u help me !!

[dmkdfc]

Problem solved !

[Roxytsai]

@SUPERCILEX I'm not familiar with kotlin. Do you have example code on java? Thanks for the great help.

[SUPERCILEX]

@Roxytsai unfortunately not since the app is in production. It would be a great way to dip your feet in Kotlin though! And if you have questions, feel free to ask them. 😀

[Roxytsai]

@SUPERCILEX Thanks for your suggestion, I'm studying Kotlin now. Owing to Robot-Scouter app still too complex for me, do you have Quickstart code about how to solve scroll position in FirestoreRecyclerAdapter by using ObservableSnapshotArray.
Anyway, thanks for your feedback.

[Roxytsai]

@SUPERCILEX Thanks for your suggestion, I resolved it! Many thanks~

[pz64]

In my case, I didn't want move to a specific position, instead I just wanted to keep the original position after returning from a different Activity or returning from background.

I just added this empty listener and it's working.

 listAdapter.snapshots.addChangeEventListener(object : ChangeEventListener {
        override fun onChildChanged(
            type: ChangeEventType,
            snapshot: DocumentSnapshot,
            newIndex: Int,
            oldIndex: Int
        ) {
        }

        override fun onDataChanged() {
        }

        override fun onError(e: FirebaseFirestoreException) {
        }
    })

Here listAdapter is FirestoreRecyclerAdapter.