安卓向RecyclerView添加头部不会显示所有列表项

public class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
    private static final int TYPE_HEADER = 1;
    private List<String> dataList;
    private View headerView;

    public MyAdapter(List<String> dataList, View headerView) {
        this.dataList = dataList;
        this.headerView = headerView;
    }

    @Override
    public int getItemViewType(int position) {
        if (position == 0) {
            return TYPE_HEADER;
        }
        return super.getItemViewType(position);
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (viewType == TYPE_HEADER) {
            LayoutInflater inflater = LayoutInflater.from(parent.getContext());
            View view = inflater.inflate(R.layout.header_layout, parent, false);
            return new HeaderViewHolder(view);
        }
        // 返回其他类型的ViewHolder
        // ...
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (holder instanceof HeaderViewHolder) {
            // 绑定头部内容
            // ...
        } else {
            // 绑定其他类型的内容
            // ...
        }
    }

    @Override
    public int getItemCount() {
        // 考虑头部的数量
        return dataList.size() + 1;
    }

    // 定义头部ViewHolder
    private class HeaderViewHolder extends RecyclerView.ViewHolder {
        // 头部控件的引用
        // ...

        HeaderViewHolder(View itemView) {
            super(itemView);
            // 初始化头部控件
            // ...
        }
    }
}

List<String> dataList = new ArrayList<>();
// 添加列表数据

LayoutInflater inflater = LayoutInflater.from(context);
View headerView = inflater.inflate(R.layout.header_layout, parent, false);

MyAdapter adapter = new MyAdapter(dataList, headerView);
recyclerView.setAdapter(adapter);