Why isn't my RecyclerView displaying my adapter items?

So i have a recycler view that is designed to show users sending messages to each other from my Firebase RTD. Originally it was working to show all users and the recycler items were clicked then it would show messages between the users. However, when modifying it to only view users that were in open messages with the current user, the items that populated my recycler view no longer displays and an error saying E/RecyclerView: No adapter attached; skipping layout is logged within the Run tab.

Unfortunately i can no longer undo the changes and have struggled to find the cause of my problem but have assume that it is either taking place in my adapted or activity classes.

InboxActivity.java:

public class InboxActivity extends AppCompatActivity {
private RecyclerView recyclerView;
private List<User> inboxLst;
FirebaseUser user;
DatabaseReference reference;
UserAdapter usrAdpt;
private List<String> userLst;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_inbox);
//Identify and setup recycler view
recyclerView = findViewById(R.id.rycInbox);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
userLst = new ArrayList<>();
//Get all chats between current user and and other users
user = FirebaseAuth.getInstance().getCurrentUser();
reference = FirebaseDatabase.getInstance().getReference("Chats");
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
userLst.clear();
for (DataSnapshot snp : dataSnapshot.getChildren()){
Chat chat = snp.getValue(Chat.class);
if (chat.getSender().equals(user.getUid())){
userLst.add(chat.getReceiver());
}
if (chat.getReceiver().equals(user.getUid())){
userLst.add(chat.getSender());
}
}
readChat();
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
private void readChat() {
inboxLst = new ArrayList<>();
reference = FirebaseDatabase.getInstance().getReference("Users");
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
userLst.clear();
for (DataSnapshot snp : dataSnapshot.getChildren()) {
User usr = snp.getValue(User.class);
//Display users that are currently in an open chat
for (String id : userLst){
if(usr.getId().equals(id)){
if(inboxLst.size() != 0){
for (User usrl : inboxLst){
if(!usr.getId().equals(usrl.getId())){
inboxLst.add(usr);
}
}
}else{
inboxLst.add(usr);
}
}
}
}
//Set the adapter for the recycler view once using the chat information retrieved from firebase database
usrAdpt = new UserAdapter(InboxActivity.this,inboxLst);
recyclerView.setAdapter(usrAdpt);
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) { }
});
}
}

UserAdapter.java:

public class UserAdapter extends RecyclerView.Adapter<UserAdapter.ViewHolder> {
private Context cont;
private List<User> nUser;
public UserAdapter(Context cont, List<User> nUser){
this.cont = cont;
this.nUser = nUser;
}
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(cont).inflate(R.layout.lst_layout_inbox, parent, false);
return new ViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
User user = nUser.get(position);
holder.username.setText(user.getUsername());
holder.usrLst.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(cont, MessageActivity.class);
intent.putExtra("userid",user.getId());
cont.startActivity(intent);
}
});
}
@Override
public int getItemCount() {
return nUser.size();
}
public class ViewHolder extends RecyclerView.ViewHolder{
public TextView username;
RelativeLayout usrLst;
public ViewHolder(View itemView){
super(itemView);
username = itemView.findViewById(R.id.usrName);
usrLst = itemView.findViewById(R.id.usrCard);
}
}
}

The only catchup in your question is, in the following method:

     @Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
userLst.clear(); // <------ WHY YOU CLEAR LIST HERE??? COMMENT THIS ----------
for (DataSnapshot snp : dataSnapshot.getChildren()) {
User usr = snp.getValue(User.class);
//Display users that are currently in an open chat
for (String id : userLst){
if(usr.getId().equals(id)){
if(inboxLst.size() != 0){
for (User usrl : inboxLst){
if(!usr.getId().equals(usrl.getId())){
inboxLst.add(usr);
}
}
}else{
inboxLst.add(usr);
}
}
}
}
//Set the adapter for the recycler view once using the chat information retrieved from firebase database
usrAdpt = new UserAdapter(InboxActivity.this,inboxLst);
recyclerView.setAdapter(usrAdpt);
}

why you do userLst.clear(); ?

Since in OnCreate() method you populate userLst and call readChat(). And in onDataChange() you clear the userLst and then afterwards you try to iterate over the userLst to Display users that are currently in an open chat.

I would suggest to comment this userLst.clear(); and after setting items call notifyDataSetChanged()

Try these things:

• Set the adapter in onCreate.
• and in the onDataChanged listener, update the ArrayList and call notifyDataSetChanged().

This should help