Firebase Realtime Database Pagination in Recyclerview

pagination is also known as load more functionality or infinite loading

We can both implement Linealayout or Grid Layout.

I am using a fragment to implementing this but you can do with activity also.

UsersFragment.Java

public class UserFragment extends Fragment
{

    View UserFragment;
    RecyclerView recycler_view_user;
  //   LinearLayoutManager manager;    //for linear layout
    NewAdapter adapter;
    String last_key="",last_node="";
    boolean isMaxData=false,isScrolling=false;
    int ITEM_LOAD_COUNT= 10;
    ProgressBar progressBar;

    int currentitems,tottalitems,scrolledoutitems;


    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState)
    {
        UserFragment=inflater.inflate(R.layout.fragment_user,container,false);

        recycler_view_user=UserFragment.findViewById(R.id.recycler_view_user);
        progressBar=UserFragment.findViewById(R.id.progressBar1);
        getLastKeyFromFirebase(); //43

     //   manager=new LinearLayoutManager(getContext());

         GridLayoutManager manager = new GridLayoutManager(getContext(),2);   //for grid layout


        adapter=new NewAdapter(getContext());

        recycler_view_user.setAdapter(adapter);
        recycler_view_user.setLayoutManager(manager);
        getUsers();
        recycler_view_user.addOnScrollListener(new RecyclerView.OnScrollListener()
        {
            @Override
            public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState)
            {
                super.onScrollStateChanged(recyclerView, newState);
                if(newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL)
                {
                    isScrolling=true;

                }

            }

            @Override
            public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy)
            {
                super.onScrolled(recyclerView, dx, dy);

                currentitems=manager.getChildCount();
                tottalitems=manager.getItemCount();
                scrolledoutitems=manager.findFirstVisibleItemPosition();

                if( isScrolling && currentitems + scrolledoutitems == tottalitems)
                {
                  //  Toast.makeText(getContext(), "fetch data", Toast.LENGTH_SHORT).show();
                    isScrolling=false;
                    //fetch data
                    progressBar.setVisibility(View.VISIBLE);
                    getUsers();

                }

            }
        });

        return UserFragment;
    }

    private void getUsers()
    {
        if(!isMaxData) // 1st fasle
        {
            Query query;

            if (TextUtils.isEmpty(last_node))
                   query = FirebaseDatabase.getInstance().getReference()
                             .child("Users")
                             .orderByKey()
                             .limitToFirst(ITEM_LOAD_COUNT);
            else
                query = FirebaseDatabase.getInstance().getReference()
                        .child("Users")
                        .orderByKey()
                        .startAt(last_node)
                        .limitToFirst(ITEM_LOAD_COUNT);

            query.addListenerForSingleValueEvent(new ValueEventListener()
            {
                @Override
                public void onDataChange(@NonNull DataSnapshot snapshot)
                {
                    if(snapshot.hasChildren())
                    {

                        List<Users> newUsers = new ArrayList<>();
                        for (DataSnapshot userSnapshot : snapshot.getChildren())
                        {
                            newUsers.add(userSnapshot.getValue(Users.class));
                        }

                        last_node =newUsers.get(newUsers.size()-1).getId();    //10  if it greater than the toatal items set to visible then fetch data from server

                        if(!last_node.equals(last_key))
                            newUsers.remove(newUsers.size()-1);    // 19,19 so to renove duplicate removeone value
                           else
                               last_node="end";

                       // Toast.makeText(getContext(), "last_node"+last_node, Toast.LENGTH_SHORT).show();

                        adapter.addAll(newUsers);
                        adapter.notifyDataSetChanged();


                    }
                    else   //reach to end no further child avaialable to show
                    {
                        isMaxData=true;
                    }

                  progressBar.setVisibility(View.GONE);

                }

                @Override
                public void onCancelled(@NonNull DatabaseError error)
                {

                }
            });

        }

        else
        {
            progressBar.setVisibility(View.GONE); //if data end
        }
    }

    private void getLastKeyFromFirebase()
    {
        Query getLastKey= FirebaseDatabase.getInstance().getReference()
                .child("Users")
                .orderByKey()
                .limitToLast(1);

        getLastKey.addListenerForSingleValueEvent(new ValueEventListener()
        {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot)
            {
                for(DataSnapshot lastkey : snapshot.getChildren())
                    last_key=lastkey.getKey();
             //   Toast.makeText(getContext(), "last_key"+last_key, Toast.LENGTH_SHORT).show();

            }

            @Override
            public void onCancelled(@NonNull DatabaseError error)
            {
                Toast.makeText(getContext(), "can not get last key", Toast.LENGTH_SHORT).show();
            }
        });


    }




}

UsersFragment.Xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view_user"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:overScrollMode="never"

        />

    <ProgressBar
        android:id="@+id/progressBar1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_alignParentBottom="true"
        android:visibility="gone"
        />

</RelativeLayout>

NewAdapter.Java

public class NewAdapter extends RecyclerView.Adapter<NewAdapter.NewViewHolder>
{
    List<Users> usersList;
    Context context;

    public NewAdapter( Context context)
    {
        this.usersList = new ArrayList<>();
        this.context = context;
    }

    public void addAll(List<Users> newUsers)
    {
        int initsize=usersList.size();
        usersList.addAll(newUsers);
        notifyItemRangeChanged(initsize,newUsers.size());
    }


    public static class NewViewHolder extends RecyclerView.ViewHolder
    {
        TextView name;

        public NewViewHolder(@NonNull View itemView)
        {
            super(itemView);
            name=itemView.findViewById(R.id.name);

        }
    }

    @NonNull
    @Override
    public NewViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType)
    {
        View itemView= LayoutInflater.from(context).inflate(R.layout.user_layout_items,parent,false);
        return new NewViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull NewViewHolder holder, int position)
    {
        holder.name.setText(usersList.get(position).getName());
    }

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


}

ModelClass

Users.java

package com.xscroll.infinitescroll.Model;

public class Users
{
    private  String id,name,email;

    public Users()
    {

    }

    public Users(String id, String name, String email)
    {
        this.id = id;
        this.name = name;
        this.email = email;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

Firebase Database structure

Result: