Using RecyclerView in android studio but nothing is getting printed

This is the page where i want to print all the usernames and price extracted from Parse dashboard

public class HomePage extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home_page);
final RecyclerView list=(RecyclerView)findViewById(R.id.list);
list.setLayoutManager(new LinearLayoutManager(this));
final ArrayList<String> username = new ArrayList<String>();
final ArrayList<String> netPrice = new ArrayList<String>();
ParseQuery<ParseObject> query=new ParseQuery<ParseObject>("Image");
query.findInBackground(new FindCallback<ParseObject>() {
@Override
public void done(List<ParseObject> objects, ParseException e) {
if (e==null){
if (objects.size()>0) {
for(ParseObject object : objects){
String user=object.getString("username");
String price=object.getString("price");
username.add(user);
netPrice.add(price);
}
}
}
else{
e.printStackTrace();
}
}
});
list.setAdapter(new ListAdapter(username,netPrice));
}
}

This is my Adapter named ListAdapter

public class ListAdapter extends RecyclerView.Adapter {
private ArrayList<String>data1;
private ArrayList<String>data2;
public ListAdapter(ArrayList<String> data1, ArrayList<String> data2){
this.data1=data1;
this.data2=data2;
}
@NonNull
@Override
public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
LayoutInflater inflater=LayoutInflater.from(parent.getContext());
View view= inflater.inflate(R.layout.list_layout,parent,false);
return new ListViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
String title1=data1.get(position);
final TextView viewById1 = holder.itemView.findViewById(R.id.text1);
viewById1.setText(title1);
String title2=data2.get(position);
final TextView viewById2 = holder.itemView.findViewById(R.id.text2);
viewById2.setText(title2);
}
@Override
public int getItemCount() {
return data1.size();
}
public class ListViewHolder extends RecyclerView.ViewHolder {
public ListViewHolder(View itemView) {
super(itemView);
}
}
}

This shows no error but nothing is getting printed.
I have passed ArrayList in my Adapter, am I allowed to that?
please help, I am struck badly trying to do this since 8 hrs.

your item count should have the size of the items you want to show

@Override
public int getItemCount() {
return 1; // return here the number of items
}

problem is with the background word.

It is calling query.findInBackground and directly after that list.setAdapter(...) which at this time, [username, netPrice] are still empty lists.
So you need to wait, until you done method is done and then set data in recycleView.

You can do that by:

1 - Create a method setRecyclerViewData which will set the recyclerview data.

2 - call setRecyclerViewData inside done after it finishes the for each loop
that way you will be sure that [username, netPrice] have some data.

query.findInBackground(new FindCallback<ParseObject>() {
    @Override
    public void done(List<ParseObject> objects, ParseException e) {
        if (e==null){
            if (objects.size()>0) {
                for(ParseObject object : objects){
                    String user=object.getString("username");
                    String price=object.getString("price");
                    username.add(user);
                    netPrice.add(price);
                  }
                  setRecyclerView(username, netPrice);
             }
             else{
                 log.d("Tag", "Objects size = 0");
             }
         }
         else{
             e.printStackTrace();
         }
    }
});

private void setRecyclerView(ArrayList<String> username, ArrayList<String> netPrice){
    list.setAdapter(newListAdapter(username,netPrice));
}

plus thing don't usually go this way in recylerview adapter, it is not showing error OK, but this is not the convention.

The reason you are seeing an empty screen is because your adapter contains no data, after getting the data in query.findInBackground, you don't notify the adapter that there is a new data.

So, what you need to do is

First, store your adapter instance into a variable

    @Override
protected void onCreate(Bundle savedInstanceState) {
...
final ArrayList<String> username = new ArrayList<String>();
final ArrayList<String> netPrice = new ArrayList<String>();
ListAdapter listAdapter = new ListAdapter(username,netPrice); // Add this line
...
list.setAdapter(listAdapter);
}

Then, in your query.findInBackground notify the adapter that there is a new data

        query.findInBackground(new FindCallback<ParseObject>() {
@Override
public void done(List<ParseObject> objects, ParseException e) {
if (e==null){
if (objects.size()>0) {
for(ParseObject object : objects){
String user=object.getString("username");
String price=object.getString("price");
username.add(user);
netPrice.add(price);
}
listAdapter.notifyDataSetChanged(); // Add this line
}
}
else{
e.printStackTrace();
}
}
});