Sectioned RecyclerView

Example.java

public class Example {
    private static final class SectionViewHolder extends RecyclerView.ViewHolder {
        private final TextView title;
        public SectionViewHolder(View view) {
            super(view);
            title = (TextView)view.findViewById(R.id.title);
        }

        public void bind(String section) {
            title.setText(section);
        }
    }

    private static final class RowViewHolder extends RecyclerView.ViewHolder {
        private final TextView title;
        public RowViewHolder(View view) {
            super(view);
            title = (TextView)view.findViewById(R.id.title);
        }

        public void bind(Data data) {
            title.setText(data.label);
        }
    }
    
    private static class DataAdapter extends SectionedRecyclerViewAdapter {
        private final List<List<Data>> data;
        private final Context context;
        private final LayoutInflater inflater;

        public DataAdapter(Context context) {
            this.context = context;
            this.inflater = LayoutInflater.from(context);
            this.data = new ArrayList<>();
        }

        public void setData(List<List<Data>> data) {
            this.data.clear();
            this.data.addAll(data);
            notifyDataSetChanged();
        }

        @Override
        protected int numberOfSections() {
            return data.size();
        }

        @Override
        protected int numberOfRowsInSection(int section) {
            return data.get(section).size();
        }

        @Override
        protected RecyclerView.ViewHolder onCreateSectionViewHolder(ViewGroup parent) {
            View view = inflater.inflate(R.layout.section, parent, false);
            return new SectionViewHolder(view);
        }

        @Override
        protected RecyclerView.ViewHolder onCreateRowViewHolder(ViewGroup parent) {
            View view = inflater.inflate(R.layout.row, parent, false);
            return new RowViewHolder(view);
        }

        @Override
        protected void onBindSectionViewHolder(RecyclerView.ViewHolder holder, int section) {
            SectionViewHolder viewHolder = (SectionViewHolder)holder;
            viewHolder.bind(data.get(section).domain);
        }

        @Override
        protected void onBindRowViewHolder(RecyclerView.ViewHolder holder, int section, int row) {
            RowViewHolder viewHolder = (RowViewHolder)holder;
            viewHolder.bind(data.get(section).get(row));
        }
    }
}

SectionedRecyclerViewAdapter.java

import android.support.v7.widget.RecyclerView;
import android.view.ViewGroup;

public abstract class SectionedRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    @Override
    final public int getItemCount() {
        int count = numberOfSections();
        for (int section = 0; section < numberOfSections(); section++) {
            count += numberOfRowsInSection(section);
        }

        return count;
    }

    @Override
    public int getItemViewType(int position) {
        return isSectionHeader(position) ? 0 : 1;
    }

    @Override
    final public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return viewType == 0 ? onCreateSectionViewHolder(parent) : onCreateRowViewHolder(parent);
    }

    @Override
    final public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        int section = getSection(position);
        if (isSectionHeader(position)) {
            onBindSectionViewHolder(holder, section);
        } else {
            int row = getRow(position);
            onBindRowViewHolder(holder, section, row);
        }
    }

    protected abstract int numberOfSections();
    protected abstract int numberOfRowsInSection(int section);
    protected abstract RecyclerView.ViewHolder onCreateSectionViewHolder(ViewGroup parent);
    protected abstract RecyclerView.ViewHolder onCreateRowViewHolder(ViewGroup parent);
    protected abstract void onBindSectionViewHolder(RecyclerView.ViewHolder holder, int section);
    protected abstract void onBindRowViewHolder(RecyclerView.ViewHolder holder, int section, int row);

    protected boolean isSectionHeader(int position) {
        int current = 0;
        for (int section = 0; section < numberOfSections(); section++) {
            if (current == position) return true;
            current = (current + 1 + numberOfRowsInSection(section));
        }

        return false;
    }

    private int getSection(int position) {
        int current = 0;
        for (int section = 0; section < numberOfSections(); section++) {
            int end = (current + 1 + numberOfRowsInSection(section));
            if (position >= current && position < end)
                return section;

            current = end;
        }

        throw new IllegalArgumentException("Position " + position + " is not part of a valid section");
    }

    private int getRow(int position) {
        int current = 0;
        for (int section = 0; section < numberOfSections(); section++) {
            int end = (current + 1 + numberOfRowsInSection(section));
            if (position > current && position < end)
                return (position - current - 1);

            current = end;
        }

        throw new IllegalArgumentException("Position " + position + " does not point to a row item");
    }
}

Also, I'm missing touch handlers, which I'll add in another revision.