使用SectionedRecyclerViewAdapter的RecyclerView仅显示第一个标题

public class MySectionedAdapter extends SectionedRecyclerViewAdapter<MySectionedAdapter.ViewHolder> {

    private List<MySection> sections;

    public MySectionedAdapter(List<MySection> sections) {
        this.sections = sections;
    }

    @Override
    public int getSectionCount() {
        return sections.size();
    }

    @Override
    public int getItemCount(int sectionIndex) {
        return sections.get(sectionIndex).getItemCount();
    }

    @Override
    public void onBindHeaderViewHolder(ViewHolder holder, int sectionIndex, boolean expanded) {
        String title = sections.get(sectionIndex).getTitle();
        holder.title.setText(title);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int sectionIndex, int relativePosition, int absolutePosition) {
        String item = sections.get(sectionIndex).getItem(relativePosition);
        holder.item.setText(item);
    }

    @Override
    public ViewHolder onCreateHeaderViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.header_layout, parent, false);
        return new ViewHolder(view, true);
    }

    @Override
    public ViewHolder onCreateItemViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_layout, parent, false);
        return new ViewHolder(view, false);
    }

    static class ViewHolder extends RecyclerView.ViewHolder {
        TextView title;
        TextView item;

        ViewHolder(View itemView, boolean isHeader) {
            super(itemView);
            if (isHeader) {
                title = itemView.findViewById(R.id.header_title);
            } else {
                item = itemView.findViewById(R.id.item_text);
            }
        }
    }

    static class MySection {
        private String title;
        private List<String> items;

        public MySection(String title, List<String> items) {
            this.title = title;
            this.items = items;
        }

        public String getTitle() {
            return title;
        }

        public int getItemCount() {
            return items.size();
        }

        public String getItem(int position) {
            return items.get(position);
        }
    }
}