BetterRecyclerAdapter

public abstract class CustomSortFirebaseRecyclerAdapter<T> extends RecyclerView.Adapter implements ChildEventListener {

    protected Query mRef;
    private Class<T> mModelClass;
    private RecyclerQuestionAnswerer<T> mRecyclerQuestionAnswerer;
    protected SortedList<T> mModels;
    protected Map<String, T> mModelKeys;
    private ChildEventListener mListener;
    protected Context mContext;

    public CustomSortFirebaseRecyclerAdapter(Query ref, Class<T> modelClass, final RecyclerQuestionAnswerer<T> recyclerQuestionAnswerer) {
        mRef = ref;
        mModelClass = modelClass;
        mModelKeys = Collections.synchronizedMap(new HashMap<String, T>());
        mModels = new SortedList<T>(modelClass, new SortedListAdapterCallback<T>(this) {
            @Override
            public int compare(T lhs, T rhs) {
                return recyclerQuestionAnswerer.compare(lhs, rhs);
            }

            @Override
            public boolean areContentsTheSame(T oldItem, T newItem) {
                return recyclerQuestionAnswerer.areContentsTheSame(oldItem, newItem);
            }

            @Override
            public boolean areItemsTheSame(T item1, T item2) {
                return recyclerQuestionAnswerer.areItemsTheSame(item1, item2);
            }
        });
        mRecyclerQuestionAnswerer = recyclerQuestionAnswerer;
        mListener = mRef.addChildEventListener(this);
    }

    public void cleanup() {
        mRef.removeEventListener(mListener);
    }

    @Override
    public long getItemId(int i) {
        return mModels.get(i).hashCode();
    }

    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String previousChildName) {
        T model = dataSnapshot.getValue(CustomSortFirebaseRecyclerAdapter.this.mModelClass);
        if (mRecyclerQuestionAnswerer.include(model)) {
            final String key = dataSnapshot.getKey();
            mModelKeys.put(key, model);
            mModels.add(model);
        }
    }

    @Override
    public void onChildChanged(DataSnapshot dataSnapshot, String previousChildName) {
        final T value = dataSnapshot.getValue(mModelClass);
        final String key = dataSnapshot.getKey();
        if (mRecyclerQuestionAnswerer.include(value) && !mModelKeys.containsKey(key)) {
            onChildAdded(dataSnapshot, previousChildName);
        } else if (!mRecyclerQuestionAnswerer.include(value) && mModelKeys.containsKey(key)) {
            onChildRemoved(dataSnapshot);
        } else if (mRecyclerQuestionAnswerer.include(value) && mModelKeys.containsKey(key)){
            final T oldValue = mModelKeys.get(key);
            mModelKeys.put(key, value);
            mModels.updateItemAt(mModels.indexOf(oldValue), value);
        }
    }

    @Override
    public void onChildRemoved(DataSnapshot dataSnapshot) {
        final String key = dataSnapshot.getKey();
        final T oldModel = mModelKeys.get(key);
        mModelKeys.remove(key);
        mModels.remove(oldModel);
    }

    @Override
    public void onChildMoved(DataSnapshot dataSnapshot, String previousChildName) {
        // nop
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {
        Log.e(getClass().getName(), "Listen was cancelled, no more updates will occur");
    }

    @Override
    public int getItemCount() {
        return mModels.size();
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return onCreateViewHolderImpl(parent, viewType);
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        onBindViewHolderImpl(holder, position);
    }

    protected abstract int getEmptyTextId();

    protected abstract RecyclerView.ViewHolder onCreateViewHolderImpl(ViewGroup parent, int viewType);

    protected abstract void onBindViewHolderImpl(RecyclerView.ViewHolder vh, int position);
    
}

public interface RecyclerQuestionAnswerer<T> {
    boolean include(T model);

    int compare(T lhs, T rhs);

    boolean areContentsTheSame(T lhs, T rhs);

    boolean areItemsTheSame(T lhs, T rhs);
}