Simple Recyclerview + Viewholder

ItemListingActivity.java

package com.yatoo.activity;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.View;
import android.widget.LinearLayout;

import com.getbase.floatingactionbutton.FloatingActionButton;
import com.github.amlcurran.showcaseview.ShowcaseView;
import com.github.amlcurran.showcaseview.targets.Target;
import com.github.amlcurran.showcaseview.targets.ViewTarget;
import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.yatoo.BaseActivity;
import com.yatoo.R;
import com.yatoo.adapter.ItemsAdapter;
import com.yatoo.manager.SharedPreferenceManager;
import com.yatoo.model.Item;
import com.yatoo.utils.Constants;
import com.yatoo.utils.Utils;

import java.util.ArrayList;
import java.util.List;


public class ItemListingActivity extends BaseActivity implements View.OnClickListener{

    private ItemsAdapter itemsAdapter;
    private RecyclerView recyclerView;
    private GridLayoutManager gridLayoutManager;

    private List<Item> itemList;
    public static List<String> itemFavoriteList;

    private DatabaseReference mDatabaseReference;
    private LinearLayout progressBar;

    private FloatingActionButton floatingAddItem;
    private String userUID;

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

        getLayoutInflater().inflate(R.layout.activity_item_listing, frameLayout);
        userUID = SharedPreferenceManager.getUserUid(this);

        progressBar = (LinearLayout)findViewById(R.id.progress_bar);

        floatingAddItem = (FloatingActionButton) findViewById(R.id.add_item_call_to_action);
        floatingAddItem.setOnClickListener(this);

        getFavorites();

        Target viewTarget = new ViewTarget(R.id.add_item_call_to_action, this);
        new ShowcaseView.Builder(this)
                .setTarget(viewTarget)
                .setContentTitle(R.string.give_easily_object)
                .setContentText(R.string.add_item_tutorial_subtitle)
                .setStyle(R.style.CustomShowcaseTheme)
                .singleShot(42)
                .build();

        itemList = new ArrayList<>();
        itemFavoriteList = new ArrayList<>();

        recyclerView = (RecyclerView)findViewById(R.id.main_recyclerview);
        gridLayoutManager = new GridLayoutManager(this,  2);
        recyclerView.setLayoutManager(gridLayoutManager);

        mDatabaseReference = FirebaseDatabase.getInstance().getReference().child(Constants.FIREBASE_LOCATION_ITEMS);

        ChildEventListener childEventListener = new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                getUpdates(dataSnapshot);
            }

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

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {
                getUpdates(dataSnapshot);
            }

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

            @Override
            public void onCancelled(DatabaseError databaseError) {
                Utils.showSnack(rootView, getString(R.string.common_error_occured)+databaseError);
            }
        };

        mDatabaseReference.addChildEventListener(childEventListener);
        itemsAdapter = new ItemsAdapter(itemList);
        recyclerView.setHasFixedSize(true);
        recyclerView.setAdapter(itemsAdapter);

    }

    @Override
    public void onClick(View v) {

        switch(v.getId()){

            case R.id.add_item_call_to_action:

                Intent intent = new Intent(ItemListingActivity.this, WizardAddItem.class);
                startActivity(intent);

                break;
        }
    }

    /*@Override
    public void onClick(int position) {
        Item itemSelected = itemArrayList.get(position);
        Intent intentItemDetail = new Intent(ItemListingActivity.this, ItemDetailDisplayActivity.class);
        intentItemDetail.putExtra("ITEM_SELECTED", itemSelected);
        startActivity(intentItemDetail);
    }*/

    public void getUpdates(DataSnapshot dataSnapshot){
        Item item = dataSnapshot.getValue(Item.class);
        itemList.add(item);
        itemsAdapter.refreshItem(itemList);
        progressBar.setVisibility(View.GONE);
    }

    public void getFavorites(){
        DatabaseReference mFirebaseRef = FirebaseDatabase.getInstance().getReference().child("users").child(userUID).child("favorites");
        mFirebaseRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

                itemFavoriteList.clear();

                if(dataSnapshot.getChildrenCount() > 0){
                    Log.v(Constants.LOG_TAG, "nb: "+dataSnapshot.getChildrenCount());

                    for (DataSnapshot data : dataSnapshot.getChildren()) {
                        itemFavoriteList.add(data.child("uniqueID").getValue().toString());
                    }
                }
                Log.v("com.item", String.valueOf(itemFavoriteList));

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
            }
        });
    }
}

ItemsAdapter.java

package com.yatoo.adapter;

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import com.google.firebase.database.DatabaseReference;
import com.like.LikeButton;
import com.like.OnLikeListener;
import com.squareup.picasso.Picasso;
import com.yatoo.R;
import com.yatoo.activity.ItemListingActivity;
import com.yatoo.manager.SharedPreferenceManager;
import com.yatoo.model.Item;
import com.yatoo.utils.Utils;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;

/**
 * Created by audaxis on 01/07/16.
 */
public class ItemsAdapter extends RecyclerView.Adapter<ItemsAdapter.ItemViewHolder> {

    List<Item> itemArrayList = new ArrayList<>();

    public ItemsAdapter(List<Item> itemArrayList){
        this.itemArrayList = itemArrayList;
    }

    @Override
    public ItemViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.row_item, parent, false);
        ItemViewHolder itemViewHolder = new ItemViewHolder(view);

        return itemViewHolder;
    }

    @Override
    public void onBindViewHolder(ItemViewHolder holder, int position) {

        Item item = itemArrayList.get(position);

        //We check if the item is in the favoriteArray
        for (String s : ItemListingActivity.itemFavoriteList) {
            int i = s.indexOf(item.getUniqueID());
            if (i >= 0) {
                holder.likeButton.setLiked(true);
            }
        }

        holder.itemTitle.setText(item.getTitle());
        holder.itemLocation.setText(item.getLocation().getCity());
        holder.itemPublicationDate.setText(Utils.getHumanReadableDate(holder.itemView, new Date(item.getPublishedDate())));

        if(item.getFrontImage() != null){

            Picasso.with(holder.itemView.getContext())
                    .load(item.getFrontImage())
                    .into(holder.itemFrontImage);
        }

    }

    public void refreshItem(List<Item> items) {
        itemArrayList.clear();
        itemArrayList.addAll(items);
        this.notifyDataSetChanged();
    }

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

    public static class ItemViewHolder extends RecyclerView.ViewHolder implements OnLikeListener{

        private TextView itemTitle, itemPublicationDate, itemLocation;
        private ImageView itemFrontImage;
        private DatabaseReference mFirebaseRef;
        private String UserUID;
        private LikeButton likeButton;


        public ItemViewHolder(View itemView) {

            super(itemView);
            itemTitle = (TextView) itemView.findViewById(R.id.row_item_title_textview);
            itemPublicationDate = (TextView) itemView.findViewById(R.id.row_item_publication_date_textview);
            itemFrontImage = (ImageView) itemView.findViewById(R.id.row_item_thumbnail_imageView);
            itemLocation = (TextView) itemView.findViewById(R.id.row_item_location);
            UserUID = SharedPreferenceManager.getUserUid(itemView.getContext());
            likeButton = (LikeButton) itemView.findViewById(R.id.like_button);
        }

        @Override
        public void liked(LikeButton likeButton) {

        }

        @Override
        public void unLiked(LikeButton likeButton) {

        }
    }

}