FirebaseRecyclerAdapter

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.ViewGroup;

import com.firebase.client.ChildEventListener;
import com.firebase.client.DataSnapshot;
import com.firebase.client.FirebaseError;
import com.firebase.client.Query;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;


public abstract class FirebaseRecyclerAdapter<T> extends RecyclerView.Adapter {
    private static final int VIEW_TYPE_EMPTY_LIST_PLACEHOLDER = 0;
    private static final int VIEW_TYPE_OBJECT_VIEW = 1;

    protected Query mRef;

    protected List<String> mModelKeysList = Collections.synchronizedList(new ArrayList<String>());
    protected Map<String, T> mModelKeyMap = Collections.synchronizedMap(new HashMap<String, T>());

    private ChildEventListener mListener;

    public FirebaseRecyclerAdapter(final Query ref, final Class<T> modelClass) {
        mRef = ref;
        mModelKeysList = Collections.synchronizedList(new ArrayList<String>());
        mModelKeyMap = Collections.synchronizedMap(new HashMap<String, T>());
        mListener = mRef.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String previousChildName) {
                final String key = dataSnapshot.getKey();
                mModelKeyMap.put(key, dataSnapshot.getValue(modelClass));
                int previousIndex = mModelKeysList.indexOf(previousChildName);
                int nextIndex = previousIndex + 1;
                mModelKeysList.add(nextIndex, key);
                notifyDataSetChanged();
            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String previousChildName) {
                T newModel = dataSnapshot.getValue(modelClass);
                String modelName = dataSnapshot.getKey();
                mModelKeyMap.put(modelName, newModel);
                notifyDataSetChanged();
            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {
                final String key = dataSnapshot.getKey();
                int index = mModelKeysList.indexOf(key);
                mModelKeyMap.remove(key);
                mModelKeysList.remove(index);
                notifyDataSetChanged();
            }

            @Override
            public void onChildMoved(DataSnapshot dataSnapshot, String previousChildName) {
                String modelName = dataSnapshot.getKey();
                mModelKeyMap.put(modelName, dataSnapshot.getValue(modelClass));
                int index = mModelKeysList.indexOf(modelName);
                mModelKeysList.remove(index);
                int previousIndex = mModelKeysList.indexOf(previousChildName);
                int nextIndex = previousIndex + 1;
                mModelKeysList.add(nextIndex, modelName);
                notifyDataSetChanged();
            }

            @Override
            public void onCancelled(FirebaseError firebaseError) {

            }
        });
    }

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

    @Override
    public int getItemCount() {
        return mModelKeysList.isEmpty() ? 1 : mModelKeysList.size();
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        switch (viewType) {
            case VIEW_TYPE_EMPTY_LIST_PLACEHOLDER:
                return new EmptyViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.empty_list_item, parent, false));
            case VIEW_TYPE_OBJECT_VIEW:
                return onCreateViewHolderImpl(parent, viewType);
        }
        throw new IllegalStateException("Unimplemented viewType");
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        switch (getItemViewType(position)) {
            case VIEW_TYPE_EMPTY_LIST_PLACEHOLDER:
                ((EmptyViewHolder) holder).setEmptyText(getEmptyTextId());
                break;
            case VIEW_TYPE_OBJECT_VIEW:
                onBindViewHolderImpl(holder, position);
                break;
        }
    }

    protected abstract int getEmptyTextId();
    protected abstract RecyclerView.ViewHolder onCreateViewHolderImpl(ViewGroup parent, int viewType);
    protected abstract void onBindViewHolderImpl(RecyclerView.ViewHolder vh, int position);

    @Override
    public int getItemViewType(int position) {
        if (mModelKeysList.isEmpty()) {
            return VIEW_TYPE_EMPTY_LIST_PLACEHOLDER;
        } else {
            return VIEW_TYPE_OBJECT_VIEW;
        }
    }
}

public class EmptyViewHolder extends RecyclerView.ViewHolder {
    @InjectView(R.id.empty_view_holder_text)
    TextView mEmptyText;

    public EmptyViewHolder(View itemView) {
        super(itemView);
        ButterKnife.inject(this, itemView);
    }

    public void setEmptyText(int stringId) {
        mEmptyText.setText(stringId);
    }
}