Android: Detect when the RecyclerView reaches the bottom

Sometimes we need to detect weather a RecyclerView hits the bottom for alot of reasons, one of the most frequent is when you need to show more content of your app (pagination) when the user scrolls, just like facebook or medium.

You should be familiar with:

• Android Studio
• RecyclerView
• RecyclerView Adapter
• Polymorphism

Few days ago i was trying to implement a way to make my app fetch data from the server while the user is scrolling since there’s alot of data to parse, and fetch the whole data is a really waste of resources.

I couldn’t find any straightforward answer on Stackoverflow, and i couldn’t find any answer to do it on a Staggered Layout Manager.

So i had to find another way around it using the great power of polymorphism.

Let’s get started!

1. create an Android Studio project

You’ll need the following dependency:

compile 'com.android.support:recyclerview-v7:25.1.1'

2. In your activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="ayham.recyclerviewbottom.MainActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent">


    </android.support.v7.widget.RecyclerView>

</RelativeLayout>

3. Create an item view in your res/layout folder, i called it my_item.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="200dp"
    android:layout_margin="8dp">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="TEXT"
        android:id="@+id/text"
        android:gravity="center"
        />


</android.support

4. Create your custom adapter

The Adapter should extend

RecyclerView.Adapter<YourViewHolder>

The Adapter has 3 methods that you should override

1. onCreateViewHolder
2. onBindViewHolder
3. getItemCount

and your view holder class could be an inner class inside your adapter

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {

    List<String> strings;

    public MyAdapter(List<String> strings) {

        this.strings = strings;

    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.my_item, parent, false);

        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {

        holder.textView.setText(strings.get(position));

    }

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

    public class ViewHolder extends RecyclerView.ViewHolder{

        public TextView textView;


        public ViewHolder(View itemView) {
            super(itemView);

            textView = (TextView) itemView.findViewById(R.id.text);
        }
    }



}

5. Create an Interface

Here’s where the magic will start. create an interface, i called it OnBottomReachedListener that has one method, onBottomReached

public interface OnBottomReachedListener {

    void onBottomReached(int position);

}

6. In your adapter class

Add

OnBottomReachedListener onBottomReachedListener;

It should look like this

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {

    List<String> strings;
    OnBottomReachedListener onBottomReachedListener;

    public MyAdapter(List<String> strings) {

        this.strings = strings;

    }

Now add a set method

public void setOnBottomReachedListener(OnBottomReachedListener onBottomReachedListener){

    this.onBottomReachedListener = onBottomReachedListener;
}

On your onBindViewHolder add the following

if (position == strings.size() - 1){

    onBottomReachedListener.onBottomReached(position);

}

the adapter class should look something like this

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {

    List<String> strings;
    OnBottomReachedListener onBottomReachedListener;

    public MyAdapter(List<String> strings) {

        this.strings = strings;

    }

    public void setOnBottomReachedListener(OnBottomReachedListener onBottomReachedListener){

        this.onBottomReachedListener = onBottomReachedListener;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.my_item, parent, false);

        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {

        if (position == strings.size() - 1){

            onBottomReachedListener.onBottomReached(position);

        }

        holder.textView.setText(strings.get(position));

    }

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

    public class ViewHolder extends RecyclerView.ViewHolder{

        public TextView textView;


        public ViewHolder(View itemView) {
            super(itemView);

            textView = (TextView) itemView.findViewById(R.id.text);
        }
    }



}

7. Let’s get it to work!

In your MainActivity make a List and add some items to it and add the RecyclerView and it’s adapter just like this

public class MainActivity extends AppCompatActivity {

    List<String> strings;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        strings = new ArrayList<>();


        for (int i = 0; i < 20; i++) {
            strings.add("# " + (i + 1));
        }

        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        MyAdapter adapter = new MyAdapter(strings);
        recyclerView.setLayoutManager(new LinearLayoutManager(getBaseContext()));
        recyclerView.setAdapter(adapter);

    }
}

Finally add set the listener

adapter.setOnBottomReachedListener(new OnBottomReachedListener() {
    @Override
    public void onBottomReached(int position) {
        //your code goes here
    }
});

Your MainActivity should look like this

public class MainActivity extends AppCompatActivity {

    List<String> strings;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        strings = new ArrayList<>();


        for (int i = 0; i < 20; i++) {
            strings.add("# " + (i + 1));
        }

        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        MyAdapter adapter = new MyAdapter(strings);
        recyclerView.setLayoutManager(new LinearLayoutManager(getBaseContext()));
        recyclerView.setAdapter(adapter);

        adapter.setOnBottomReachedListener(new OnBottomReachedListener() {
            @Override
            public void onBottomReached(int position) {
                //your code goes here
            }
        });

    }
}

How does this work?

Taking advantage of the design patterns, you simply define the interface and leave the implementation to other classes to make the code more organized and reusable. Note that if you don’t set the Interface in your main activity it’ll throw a NPE so make sure to handle that :) .

with ❤️