Develop Reference

How can i pass user id from my adapter to activity

i am trying to pass holders user.getID to my attendance activity how can i pass users id from my adapter to attendance activity
this is my attendance activity
reference = FirebaseDatabase.getInstance().getReference("parent");
intent = getIntent();
final String currentSubject = intent.getStringExtra("currentSubject");
reference.addValueEventListener(new ValueEventListener() {
#RequiresApi(api = Build.VERSION_CODES.O)
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
final User user = snapshot.getValue(User.class);
ZoneId zonedId = ZoneId.of("America/Montreal");
final LocalDate today = LocalDate.now(zonedId);
reference = FirebaseDatabase.getInstance().getReference("attendance").child(user.getSchoolcode()).child(grade.getText().toString() + " " + section.getText().toString()).child(currentSubject).child(today.toString()).child(userID);
reference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
HashMap<String, Object> hashMap = new HashMap<>();
hashMap.put("attendance", "yes");
reference.updateChildren(hashMap);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
i want to pass it from adapter to this
this is my adapter
public class StudentAdapter extends RecyclerView.Adapter<StudentAdapter.ViewHolder> {
private Context context;
private List<User> users;
public StudentAdapter(Context context, List<User> users) {
this.context = context;
this.users = users;
}
DatabaseReference reference;
#NonNull
#Override
public ViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(context).inflate(R.layout.student_item, parent, false);
return new StudentAdapter.ViewHolder(view);
}
#Override
public void onBindViewHolder(#NonNull final ViewHolder holder, int position) {
final User user = users.get(position);
holder.studentName.setText(user.getStudentname() + " " + user.getLastname());
}
#Override
public int getItemCount() {
return users.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
public TextView studentName;
public Switch aSwitch;
public ViewHolder(View itemView) {
super(itemView);
studentName = itemView.findViewById(R.id.studentName);
aSwitch = itemView.findViewById(R.id.attendanceSwitch);
}
}
this is my adapter which holds the recyclerview,i am trying to get id of users viewed on attendance activities recyclerview

A way that you can use is callback :
In your adapter define an interface like this :
public class StudentAdapter extends RecyclerView.Adapter<StudentAdapter.ViewHolder> {
private SendCallBack mCallback;
interface SendCallBack {
void send(int id);
}
//Initial callback in constructor
public StudentAdapter(Context context, List<User> users,SendCallBack callback) {
this.context = context;
this.users = users;
mCallback = callback;
}
//Now in where that you want to pass data use this
mCallback.send(user.getID);
}
Now in your activity implement the callback like this :
public class YourActivty implements YourAdapter.SendCallback {
#Override
public void send(int id) {
}
//For pass callBack for your adapter constructor use this
}
For other ways you can use this link.

How not to show user that is online in recyclerview

I am currently trying to create a messaging app.The users who have registered on to my app are showed in users tab but along with those users the user who is currently logged into my app also sees himself in users tab .I don't want user to see himself in users tab.
My code
UserAdapter.java
public class UserAdapter extends RecyclerView.Adapter<UserAdapter.ViewHolder> {
private Context mContext;
private List<User> mUsers;
private boolean ischat;
public UserAdapter(Context mContext, List<User> mUsers,boolean ischat) {
this.mContext = mContext;
this.mUsers = mUsers;
this.ischat=ischat;
}
#NonNull
#Override
public UserAdapter.ViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View view= LayoutInflater.from(mContext).inflate(R.layout.user_item,parent,false);
return new UserAdapter.ViewHolder(view);
}
#Override
public void onBindViewHolder(#NonNull UserAdapter.ViewHolder holder, int position) {
final User user=mUsers.get(position);
holder.username.setText(user.getFirst());
if (user.getImageURL().equals("default")){
holder.profile_image.setImageResource(R.mipmap.ic_launcher);
} else {
Glide.with(mContext).load(user.getImageURL()).into(holder.profile_image);
}
if (ischat){
if (user.getStatus().equals("online")){
holder.img_on.setVisibility(View.VISIBLE);
holder.img_off.setVisibility(View.GONE);
} else {
holder.img_on.setVisibility(View.GONE);
holder.img_off.setVisibility(View.VISIBLE);
}
} else {
holder.img_on.setVisibility(View.GONE);
holder.img_off.setVisibility(View.GONE);
}
holder.itemView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent=new Intent(mContext, MessageActivity.class);
intent.putExtra("UserName",user.getFirst());
intent.putExtra("userid", user.getId());
mContext.startActivity(intent);
}
});
}
#Override
public int getItemCount() {
return mUsers.size();
}
public class ViewHolder extends RecyclerView.ViewHolder{
public TextView username;
public ImageView profile_image;
private ImageView img_on;
private ImageView img_off;
public ViewHolder(#NonNull View itemView) {
super(itemView);
username=itemView.findViewById(R.id.username);
profile_image=itemView.findViewById(R.id.profile_image);
img_on = itemView.findViewById(R.id.img_on);
img_off = itemView.findViewById(R.id.img_off);
}
}
}
UsersFragment.java
public class UsersFragment extends Fragment {
private RecyclerView recyclerView;
private UserAdapter mUserAdapter;
private List<User> mUsers;
String TAG = "MyTag";
public UsersFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_users, container, false);
recyclerView = view.findViewById(R.id.recycler_view);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
mUsers = new ArrayList<>();
readUser();
return view;
}
private void readUser() {
final FirebaseUser firebaseUser=FirebaseAuth.getInstance().getCurrentUser();
DatabaseReference reference= FirebaseDatabase.getInstance().getReference("Users");
reference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
mUsers.clear();
for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
User user=snapshot.getValue(User.class);
mUsers.add(user);
}
mUserAdapter=new UserAdapter(getContext(),mUsers,false);
recyclerView.setAdapter(mUserAdapter);
mUserAdapter.notifyDataSetChanged();
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
}

Make condition to check if whether current login user is not not equals to the key node then it will add users in array
reference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
mUsers.clear();
for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
if(!FirebaseAuth.getInstance().getCurrentUser().getUid().equals(snapshot.getId())){
User user=snapshot.getValue(User.class);
mUsers.add(user);
}
}
mUserAdapter=new UserAdapter(getContext(),mUsers,false);
recyclerView.setAdapter(mUserAdapter);
mUserAdapter.notifyDataSetChanged();
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});

Unable to pass intent.Extra from UserAdapter to c_Message_Activity

public class UserAdapter extends RecyclerView.Adapter<UserAdapter.ViewHolder> {
private Context mContext;
private List<User> mUsers;
public UserAdapter(Context mContext, List<User> mUsers){
this.mUsers = mUsers;
this.mContext = mContext;
}
#NonNull
#Override
public ViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(mContext).inflate(R.layout.student_item, parent, false);
return new UserAdapter.ViewHolder(view);
}
#Override
public void onBindViewHolder(#NonNull ViewHolder holder, int position) {
final User user = mUsers.get(position);
holder.std_name.setText(user.getName());
if(user.getImage() != null && user.getImage().equals("default")){
holder.std_profile_image.setImageResource(R.mipmap.ic_launcher);
}else{
Glide.with(mContext).load(user.getImage()).into(holder.std_profile_image);
}
holder.itemView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(mContext, c_Message_Activity.class);
intent.putExtra("userid", user.getId());
mContext.startActivity(intent);
}
});
}
#Override
public int getItemCount() {
return mUsers.size();
}
public class ViewHolder extends RecyclerView.ViewHolder{
public TextView std_name;
public ImageView std_profile_image;
public ViewHolder(View itemview){
super(itemview);
std_name = itemview.findViewById(R.id.std_name);
std_profile_image = itemview.findViewById(R.id.std_profile_image);
}
}
}
Activity Code :
public class c_Message_Activity extends AppCompatActivity {
CircleImageView s_profile_image;
TextView s_profile_name;
FirebaseUser fuser;
DatabaseReference reference;
Intent intent;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.c_message_activity);
Toolbar toolbar = findViewById(R.id.c_chat_toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setTitle("");
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
toolbar.setNavigationOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
finish();
}
});
s_profile_image = findViewById(R.id.s_profile_image);
s_profile_name = findViewById(R.id.s_profile_name);
intent = getIntent();
String userid = intent.getStringExtra("userid");
fuser = FirebaseAuth.getInstance().getCurrentUser();
reference = FirebaseDatabase.getInstance().getReference("User").child(userid);
reference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
User user = dataSnapshot.getValue(User.class);
s_profile_name.setText(user.getName());
if(user.getImage() != null && user.getImage().equals("default")){
s_profile_image.setImageResource(R.mipmap.ic_launcher);
}else {
Glide.with(c_Message_Activity.this).load(user.getImage()).into(s_profile_image);
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
}
I can't pass my intent.putExtra("userid",user.getId()); to FirebaseDatabase.getInstance().getReference("User").child(userid);
Some can help me to solve this problem?
java.lang.NullPointerException: Can't pass null for argument
'pathString' in child()

Recyclerview fetch existing data after delete an item from adapter and does not update properly

I try to implement a friend request feature in the fragment using custom adapter with firebase database. The problem is when a user accepts or delete someone request, it deletes from firebase but not properly update in the RecyclerView. this problems occurred in only runtime. If I refresh the page then my problem goes away.
Let I have two friend request. If I delete 2nd data then 2nd data will gone from RecyclerView but the problem is RecyclerView shows 1st data doubles. and if I delete 1st data then 1st data goes in the 2nd row and 2nd data came into the first row.
here is my database screenshot
Fragment class-
public class NotificationFragment extends Fragment {
private RecyclerView NotificationRecyclerView;
private NotificationAdapter adapter;
private List<Friend> friendList;
public NotificationFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_notification, container, false);
NotificationRecyclerView = view.findViewById(R.id.NotificationRecyclerView);
NotificationRecyclerView.setHasFixedSize(true);
LinearLayoutManager LayoutManager = new LinearLayoutManager(getContext());
NotificationRecyclerView.setLayoutManager(LayoutManager);
friendList = new ArrayList<>();
adapter = new NotificationAdapter(getContext(), friendList);
NotificationRecyclerView.setAdapter(adapter);
readAllNotification();
return view;
}
private void readAllNotification() {
final FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("FriendRequest");
reference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
Friend friend = snapshot.getValue(Friend.class);
if (firebaseUser.getUid().equals(friend.getReceiverID())) {
friendList.add(friend);
}
}
Collections.reverse(friendList);
adapter.notifyDataSetChanged();
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
}
Custom Adapter -
public class NotificationAdapter extends RecyclerView.Adapter<NotificationAdapter.NotificationViewHolder> {
private Context context;
private List<Friend> friendList;
public NotificationAdapter(Context context, List<Friend> friendList) {
this.context = context;
this.friendList = friendList;
}
#NonNull
#Override
public NotificationViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(context).inflate(R.layout.single_notification_item, parent, false);
return new NotificationAdapter.NotificationViewHolder(view);
}
#Override
public void onBindViewHolder(#NonNull final NotificationViewHolder holder, final int position) {
final Friend friend = friendList.get(position);
getUserInfo(holder.profileImage, holder.NotificationUserName, friend.getSenderID());
holder.cancelRequestButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
FirebaseDatabase.getInstance().getReference("FriendRequest")
.child(friend.getRequestID()).removeValue().addOnCompleteListener(new OnCompleteListener<Void>() {
#Override
public void onComplete(#NonNull Task<Void> task) {
removeItem(position);
Toast.makeText(context, "removed", Toast.LENGTH_SHORT).show();
}
});
}
});
}
public void removeItem(int position) {
friendList.remove(position);
notifyDataSetChanged();
}
#Override
public int getItemCount() {
return friendList.size();
}
private void getUserInfo(final CircleImageView prfileImage, final TextView NotificationUserName, String senderID) {
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users").child(senderID);
reference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
Users users = dataSnapshot.getValue(Users.class);
NotificationUserName.setText(users.getUserName());
Picasso.with(context).load(users.getImageUrl()).into(prfileImage);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
public class NotificationViewHolder extends RecyclerView.ViewHolder {
private TextView NotificationUserName;
private Button cancelRequestButton;
private CircleImageView profileImage;
public NotificationViewHolder(#NonNull View itemView) {
super(itemView);
NotificationUserName = itemView.findViewById(R.id.NotificationUserName);
cancelRequestButton = itemView.findViewById(R.id.cancelRequestBtn);
profileImage = itemView.findViewById(R.id.profileImage);
}
}
}
My APP Problems screenshot -
let I have two request
1) if I delete 2nd data 1st data show doubles:
2) if I delete 1st data, 1st data goes into 2nd row and 2nd data came into 1st row:

Replace
removeItem(position);
with
removeItem(holder.getAdapterPosition());

You initialize your recyclerView and adapter in onCreateView which was not appropriate.You have to override the method onViewCreated then initialize your recyclerView and adapter.try like this
public class NotificationFragment extends Fragment {
private RecyclerView NotificationRecyclerView;
private NotificationAdapter adapter;
private List<Friend> friendList;
public NotificationFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_notification, container, false);
return view;
}
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
NotificationRecyclerView = view.findViewById(R.id.NotificationRecyclerView);
NotificationRecyclerView.setHasFixedSize(true);
LinearLayoutManager LayoutManager = new LinearLayoutManager(getContext());
NotificationRecyclerView.setLayoutManager(LayoutManager);
friendList = new ArrayList<>();
adapter = new NotificationAdapter(getContext(), friendList);
NotificationRecyclerView.setAdapter(adapter);
readAllNotification();
}
private void readAllNotification() {
final FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("FriendRequest");
reference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
Friend friend = snapshot.getValue(Friend.class);
if (firebaseUser.getUid().equals(friend.getReceiverID())) {
friendList.add(friend);
}
}
Collections.reverse(friendList);
adapter.notifyDataSetChanged();
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
Ok I just noticed you passed a parameter in removeItem method using holder.getAdapterPosition() which is causing your problem.Try to pass the position which is provided by public void onBindViewHolder(#NonNull final NotificationViewHolder holder, final int position).So the basic error is when you are in onBindViewHolder you don't need to use holder.getAdapterPosition() because onBindViewHolder already giving you the position
In your removeItem method use notifyDataSetChanged instead of notifyItemRemoved(position)
try like this
#Override
public void onBindViewHolder(#NonNull final NotificationViewHolder holder, final int position) {
final Friend friend = friendList.get(position);
holder.cancelRequestButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
FirebaseDatabase.getInstance().getReference("FriendRequest").child(friend.getRequestID()).removeValue().addOnCompleteListener(new OnCompleteListener<Void>() {
#Override
public void onComplete(#NonNull Task<Void> task) {
removeItem(position);
Toast.makeText(context, "removed", Toast.LENGTH_SHORT).show();
}
});
}
});
}
public void removeItem(int position) {
friendList.remove(position);
notifyDataSetChanged();
}

How do I make recyclerView that retrives data from firebase, using getKey()?

I would like to know how can I do a recyclerView that shows data that I got from this database reference:
Salas= new ArrayList<String>();
DatabaseReference referenceSalas = FirebaseDatabase.getInstance().getReference("salas/");
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("usuarios/");
FirebaseAuth autenticacao = FirebaseAuth.getInstance();
String emailUsu = autenticacao.getCurrentUser().getEmail();
reference.orderByChild("email").equalTo(emailUsu).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot datas : dataSnapshot.getChildren()) {
nomeProf = datas.child("nome").getValue().toString();
referenceSalas.orderByChild("nomeProf").equalTo(nomeProf).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot datas : dataSnapshot.getChildren()) {
Salas.add(datas.getKey());
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
throw databaseError.toException();
}
});
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
throw databaseError.toException();
}
});
I tried to do the RecyclerView like this:
public class salasFragment extends Fragment {
private RecyclerView mRecycleViewSalas;
private adapterSalas adapterSalas;
private ArrayList<salas> listaSalas= new ArrayList<>();
private LinearLayoutManager linearLayoutManager;
private TextView txtSalas, txtTeste;
private String nomeProf;
private String teste="", piru;
private DatabaseReference reference = FirebaseDatabase.getInstance().getReference("usuarios/");
private DatabaseReference referenceSalas = FirebaseDatabase.getInstance().getReference("salas/");
private ValueEventListener valueEventListenerSalas;
ArrayList<String> salasAula = new ArrayList<String>();
public salasFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_salas, container, false);
final Context context = view.getContext();
txtSalas= view.findViewById(R.id.txtSalas);
txtTeste= view.findViewById(R.id.txtTeste);
mRecycleViewSalas= view.findViewById(R.id.recyclerSalas);
adapterSalas= new adapterSalas(listaSalas, context);
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(context);
mRecycleViewSalas.setLayoutManager(layoutManager);
mRecycleViewSalas.setHasFixedSize(true);
mRecycleViewSalas.setAdapter(adapterSalas);
return view; }
#Override
public void onStart() {
super.onStart();
recuperarSalas();
}
#Override
public void onStop() {
super.onStop();
reference.removeEventListener(valueEventListenerSalas);
}
public void recuperarSalas(){
FirebaseAuth autenticacao = FirebaseAuth.getInstance();
String emailUsu = autenticacao.getCurrentUser().getEmail();
valueEventListenerSalas = reference.orderByChild("email").equalTo(emailUsu).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot datas : dataSnapshot.getChildren()) {
nomeProf = datas.child("nome").getValue().toString();
referenceSalas.orderByChild("nomeProf").equalTo(nomeProf).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot datas : dataSnapshot.getChildren()) {
salas salas=datas.getKey(salas.class);
listaSalas.add(salas);
}
adapterSalas.notifyDataSetChanged();
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
throw databaseError.toException();
}
});
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
throw databaseError.toException();
}
});
}
}
my adapter:
public class adapterSalas extends RecyclerView.Adapter<adapterSalas.myViewHolder> {
private List<salas> Salas;
private Context context;
public adapterSalas(List<salas> listaSalas, Context c ) {
this.Salas= listaSalas;
this.context = c;
}
#NonNull
#Override
public myViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int i) {
View itemLista = LayoutInflater.from(parent.getContext()).inflate(R.layout.adapter_salas, parent, false);
return new myViewHolder(itemLista);
}
#Override
public void onBindViewHolder(#NonNull myViewHolder holder, int position) {
salas sala = Salas.get(position);
holder.btn1.setText(sala.getPrimeiro());
}
#Override
public int getItemCount() {
return Salas.size();
}
public class myViewHolder extends RecyclerView.ViewHolder{
Button btn1;
public myViewHolder(#NonNull View itemView) {
super(itemView);
btn1 = itemView.findViewById(R.id.btn1);
}
}
}
Although this line "salas salas=datas.getKey(salas.class);" does not work properly when I use "getKey", It only works when "getValue" is used. There is no way of me doing this project with "getValue" instead of "getKey". So there is any way that can make this recyclerView works properly with "getKey" ?

Have you got the data from the firebase already?
If you got the data in an arraylist already, simply plug it in an adapter (you will need to create a RecyclerView adapter, a class to describe the value of each RecyclerView items) and set it to the RecyclerView and you are good to go!

You can use FirebasRecyclerAdapter as you recyclerView adapter. check out this link for a guide on how to use it.
https://medium.com/android-grid/how-to-use-firebaserecycleradpater-with-latest-firebase-dependencies-in-android-aff7a33adb8b