Endless scrolling with RecyclerVIew

Contact.java

package codepath.com.recyclerviewfun;

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

public class Contact {
    private String mName;
    private boolean mOnline;

    public Contact(String name, boolean online) {
        mName = name;
        mOnline = online;
    }

    public String getName() {
        return mName;
    }

    public boolean isOnline() {
        return mOnline;
    }

    private static int lastContactId = 0;

    public static List<Contact> createContactsList(int numContacts, int offset) {
        List<Contact> contacts = new ArrayList<Contact>();

        for (int i = 1; i <= numContacts; i++) {
            contacts.add(new Contact("Person " + ++lastContactId + " offset: " + offset, i <= numContacts / 2));
        }

        return contacts;
    }
}

ContactsAdapter.java

package codepath.com.recyclerviewfun;

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;

import java.util.List;

// Create the basic adapter extending from RecyclerView.Adapter
// Note that we specify the custom ViewHolder which gives us access to our views
public class ContactsAdapter extends
        RecyclerView.Adapter<ContactsAdapter.ViewHolder> {

    // Store a member variable for the contacts
    private List<Contact> mContacts;

    // Pass in the contact array into the constructor
    public ContactsAdapter(List<Contact> contacts) {
        mContacts = contacts;
    }

    // Provide a direct reference to each of the views within a data item
    // Used to cache the views within the item layout for fast access
    public static class ViewHolder extends RecyclerView.ViewHolder {
        // Your holder should contain a member variable
        // for any view that will be set as you render a row
        public TextView nameTextView;
        public Button messageButton;

        // We also create a constructor that accepts the entire item row
        // and does the view lookups to find each subview
        public ViewHolder(View itemView) {
            // Stores the itemView in a public final member variable that can be used
            // to access the context from any ViewHolder instance.
            super(itemView);

            nameTextView = (TextView) itemView.findViewById(R.id.contact_name);
            messageButton = (Button) itemView.findViewById(R.id.message_button);
        }
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        Context context = parent.getContext();
        LayoutInflater inflater = LayoutInflater.from(context);

        View contactView = inflater.inflate(R.layout.item_contact, parent, false);

        ViewHolder viewHolder = new ViewHolder(contactView);
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(ViewHolder viewHolder, int position) {
        Contact contact = mContacts.get(position);

        TextView textView = viewHolder.nameTextView;
        textView.setText(contact.getName());

        Button button = viewHolder.messageButton;

        if (contact.isOnline()) {
            button.setText("Message");
            button.setEnabled(true);
        }
        else {
            button.setText("Offline");
            button.setEnabled(false);
        }
    }

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

EndlessRecyclerViewScrollListener.java

package codepath.com.recyclerviewfun;

import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

public abstract class EndlessRecyclerViewScrollListener extends RecyclerView.OnScrollListener {
    // The minimum amount of items to have below your current scroll position
    // before loading more.
    private int visibleThreshold = 5;
    // The current offset index of data you have loaded
    private int currentPage = 0;
    // The total number of items in the dataset after the last load
    private int previousTotalItemCount = 0;
    // True if we are still waiting for the last set of data to load.
    private boolean loading = true;
    // Sets the starting page index
    private int startingPageIndex = 0;

    private LinearLayoutManager mLinearLayoutManager;

    public EndlessRecyclerViewScrollListener(LinearLayoutManager layoutManager) {
        this.mLinearLayoutManager = layoutManager;
    }

    // This happens many times a second during a scroll, so be wary of the code you place here.
    // We are given a few useful parameters to help us work out if we need to load some more data,
    // but first we check if we are waiting for the previous load to finish.
    @Override
    public void onScrolled(RecyclerView view, int dx, int dy) {
        int lastVisibleItem = mLinearLayoutManager.findLastVisibleItemPosition();
        int totalItemCount = mLinearLayoutManager.getItemCount();

        // If the total item count is zero and the previous isn't, assume the
        // list is invalidated and should be reset back to initial state
        if (totalItemCount < previousTotalItemCount) {
            this.currentPage = this.startingPageIndex;
            this.previousTotalItemCount = totalItemCount;
            if (totalItemCount == 0) {
                this.loading = true;
            }
        }
        // If it’s still loading, we check to see if the dataset count has
        // changed, if so we conclude it has finished loading and update the current page
        // number and total item count.
        if (loading && (totalItemCount > previousTotalItemCount)) {
            loading = false;
            previousTotalItemCount = totalItemCount;
        }

        // If it isn’t currently loading, we check to see if we have breached
        // the visibleThreshold and need to reload more data.
        // If we do need to reload some more data, we execute onLoadMore to fetch the data.
        if (!loading && totalItemCount <= (lastVisibleItem + visibleThreshold)) {
            currentPage++;
            onLoadMore(currentPage, totalItemCount);
            loading = true;
        }
    }

    // Defines the process for actually loading more data based on page
    public abstract void onLoadMore(int page, int totalItemsCount);

}

MainActivity.java

package codepath.com.recyclerviewfun;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.view.View;

import java.util.List;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        RecyclerView rvItems = (RecyclerView) findViewById(R.id.rvContacts);
        final List<Contact> allContacts = Contact.createContactsList(10, 0);
        final ContactsAdapter adapter = new ContactsAdapter(allContacts);
        rvItems.setAdapter(adapter);
        final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        rvItems.setLayoutManager(linearLayoutManager);
        rvItems.addOnScrollListener(new EndlessRecyclerViewScrollListener(linearLayoutManager) {
            @Override
            public void onLoadMore(int page, int totalItemsCount) {
                List<Contact> moreContacts = Contact.createContactsList(10, page);
                int curSize = adapter.getItemCount();
                allContacts.addAll(moreContacts);
                adapter.notifyItemRangeInserted(curSize, allContacts.size() - 1);
            }
        });
    }
    

}