About.java

public class About {

    private String titulo;
    private String subtitulo;

    public About(String titulo, String subtitulo) {
        this.titulo = titulo;
        this.subtitulo = subtitulo;
    }

    public String getTitulo() {
        return titulo;
    }

    public void setTitulo(String titulo) {
        this.titulo = titulo;
    }

    public String getSubtitulo() {
        return subtitulo;
    }

    public void setSubtitulo(String subtitulo) {
        this.subtitulo = subtitulo;
    }


}

ActivityTaskList.java

/*imports here*/
public class ActivityTaskList extends AppCompactActivity {
    @InjectView(R.id.index_list)
    RecyclerView indexList;

    private ArrayList<About> list;
    
    FinalAdapter finalAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.content_index);
        ButterKnife.inject(this);

        list = new ArrayList<>();
        for (int i = 0; i < 50; i++) {
            /*simple class task*/
            list.add(new About("Task " + i, "Task X"));
        }
        
        finalAdapter = new FinalAdapter(list);

        //tiene datos fijos
        indexList.setHasFixedSize(true);
        
        indexList.setAdapter(finalAdapter);

        indexList.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));
        //indexList.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL_LIST));
        indexList.setItemAnimator(new DefaultItemAnimator());

    }

    public void nuevoItem(View v) {
        
        list.add(new About("Task x", "Task X"));
        finalAdapter.notifyItemChanged(1);

        //util.snackbarShort(v, "Mensaje de Prueba");
    }

content_index.xml

<?xml version="1.0" encoding="UTF-8"?>
<LinearLayout android:orientation="vertical" android:layout_height="match_parent" android:layout_width="match_parent" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:android="http://schemas.android.com/apk/res/android">

<Button android:layout_height="wrap_content" android:layout_width="wrap_content" android:onClick="nuevoItem" android:text="AGREGAR"/>

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

</LinearLayout>

FinalAdapter.java

public class FinalAdapter extends RecyclerView.Adapter<FinalAdapter.TaskViewHolder> {

    private ArrayList<About> listado;

    public FinalAdapter(ArrayList<About> listado) {
        this.listado = listado;
    }

    @Override
    public TaskViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        /*layout = linearlayout wrapping a textview*/
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_single_line, parent, false);

        TaskViewHolder vh = new TaskViewHolder(v);

        return vh;
    }

    @Override
    public void onBindViewHolder(TaskViewHolder holder, int position) {
        About t = listado.get(position);
        holder.txtListitem.setText(t.getTitulo());
    }

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

    static class TaskViewHolder extends RecyclerView.ViewHolder {

        @InjectView(R.id.txt_listitem)
        TextView txtListitem;

        public TaskViewHolder(View itemView) {
            super(itemView);
            ButterKnife.inject(this,itemView);
        }

    }
}

list_item_single_line.xml

<?xml version="1.0" encoding="UTF-8"?>
<LinearLayout android:layout_height="wrap_content" android:layout_width="wrap_content" android:orientation="vertical" xmlns:android="http://schemas.android.com/apk/res/android">

<TextView android:layout_height="wrap_content" android:layout_width="match_parent" android:id="@+id/txt_listitem"/>

</LinearLayout>