How to retain RecyclerView's position after Orientation change, while using Firebase & ChildEventListener?

Question

I'm working on a simple APOD app that implements:

• RecyclerView
• CardView
• Firebase
• Picasso

The app grabs images and text from Firebase and Firebase Storage, displays them in a CardView, and sets an OnClickListener to each View. When the user clicks on an image, I open a new Activity through an Intent. The second Activity displays the original clicked image, and more info about it.

I've implemented this all using a GridLayoutManager, 1 column if the user's phone is VERTICAL, 3 columns if the user's phone is HORIZONTAL.

The problem I'm having is I can't seem to save the RecyclerView's position on orientation change. I've tried every single option that I could find, but none seem to work. The only conclusion I could come up with, is that on rotation, I'm destroying Firebase's ChildEventListener to avoid a memory leak, and once orientation is complete, Firebase re-queries the database because of the new instance of ChildEventListener.

Is there any way I can save my RecyclerView's position on orientation change? I do not want android:configChanges as it won't let me change my layout, and I've already tried saving as a Parcelable, which was unsuccessful. I'm sure it's something easy I'm missing, but hey, I'm new to developing. Any help or suggestions on my code is greatly appreciated. Thanks!

Below are my classes, which I have shortened only to the necessary code.

MainActivity

public class MainActivity extends AppCompatActivity {

private RecyclerAdapter mRecyclerAdapter;
private DatabaseReference mDatabaseReference;
private RecyclerView mRecyclerView;
private Query query;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    PreferenceManager.setDefaultValues(this, R.xml.preferences, false);
    setContentView(R.layout.activity_main);
    getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    final int columns = getResources().getInteger(R.integer.gallery_columns);

    mDatabaseReference = FirebaseDatabase.getInstance().getReference();
    query = mDatabaseReference.child("apod").orderByChild("date");

    mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);
    mRecyclerView.setHasFixedSize(true);
    mRecyclerView.setLayoutManager(new GridLayoutManager(this, columns));


    mRecyclerAdapter = new RecyclerAdapter(this, query);
    mRecyclerView.setAdapter(mRecyclerAdapter);


  }

@Override
public void onDestroy() {
    mRecyclerAdapter.cleanupListener();
  }

}

RecyclerAdapter

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ApodViewHolder> {

private final Context mContext;
private final ChildEventListener mChildEventListener;
private final Query mDatabaseReference;
private final List<String> apodListIds = new ArrayList<>();
private final List<Apod> apodList = new ArrayList<>();

public RecyclerAdapter(final Context context, Query ref) {
    mContext = context;
    mDatabaseReference = ref;


    ChildEventListener childEventListener = new ChildEventListener() {


        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            int oldListSize = getItemCount();
            Apod apod = dataSnapshot.getValue(Apod.class);

            //Add data and IDs to the list
            apodListIds.add(dataSnapshot.getKey());
            apodList.add(apod);

            //Update the RecyclerView
            notifyItemInserted(oldListSize - getItemCount() - 1);
        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {
            String apodKey = dataSnapshot.getKey();
            int apodIndex = apodListIds.indexOf(apodKey);

            if (apodIndex > -1) {

                // Remove data and IDs from the list
                apodListIds.remove(apodIndex);
                apodList.remove(apodIndex);

                // Update the RecyclerView
                notifyDataSetChanged();
            }
        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }

    };
    ref.addChildEventListener(childEventListener);
    mChildEventListener = childEventListener;

 }

   @Override
    public int getItemCount() {
    return apodList.size();
}
    public void cleanupListener() {
    if (mChildEventListener != null) {
        mDatabaseReference.removeEventListener(mChildEventListener);
    }
  }

}

Answer 1

While rotation activity get destroyed and re-created once again that means all your objects destroyed and re-created and also layout re-drawn again.

It you want to stop re-creation of activity you can use android:configChanges but it is bad practice and also not the right way.

Only thing remains now is to save position of recyclerview before rotation and get it after activity re-created.

// to save recyclerview position

 @Override
    public void onSaveInstanceState(Bundle savedInstanceState) {
      // Save UI state changes to the savedInstanceState.
      // This bundle will be passed to onCreate if the process is
      // killed and restarted.
      savedInstanceState.putInt("position", mRecyclerView.getAdapterPosition()); // get current recycle view position here.
      super.onSaveInstanceState(savedInstanceState);
    }

// to restore value

    @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    PreferenceManager.setDefaultValues(this, R.xml.preferences, false);
    setContentView(R.layout.activity_main);
    getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    final int columns = getResources().getInteger(R.integer.gallery_columns);

    mDatabaseReference = FirebaseDatabase.getInstance().getReference();
    query = mDatabaseReference.child("apod").orderByChild("date");

    mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);
    mRecyclerView.setHasFixedSize(true);
    mRecyclerView.setLayoutManager(new GridLayoutManager(this, columns));


    mRecyclerAdapter = new RecyclerAdapter(this, query);
    mRecyclerView.setAdapter(mRecyclerAdapter);
   if(savedInstanceState != null){
     // scroll to existing position which exist before rotation.
     mRecyclerView.scrollToPosition(savedInstanceState.getInt("position"));
   }  

  }

Hope these help you.