لیست ویو سفارشی

کدی که در پایین قرار میدم مربوط به کلاسی هست که یک لیست ویو 2 سطحی رو ایجاد میکنه من میخوام این لیست ویو 4 سطحی بشه.

کسی میتونه بگه باید کجای این کد رو تغییر بدم؟

import java.util.HashMap;
import java.util.List;

import android.content.Context;
import android.graphics.Typeface;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.TextView;

public class ExpandableListAdapter extends BaseExpandableListAdapter {

    private Context _context;
    private List<String> _listDataHeader;
    private HashMap<String, List<String>> _listDataChild;
    
    
    public ExpandableListAdapter(Context context, List<String> listDataHeader,
                                 HashMap<String, List<String>> listChildData) {
        this._context = context;
        this._listDataHeader = listDataHeader;
        this._listDataChild = listChildData;
    }
    
    @Override
public Object getChild(int groupPosition, int childPosititon) {
        return this._listDataChild.get(this._listDataHeader.get(groupPosition))
                .get(childPosititon);
    }
    @Override
public long getChildId(int groupPosition, int childPosition) {
        return childPosition;
    }
    
    @Override
public View getChildView(int groupPosition, final int childPosition,
                             boolean isLastChild, View convertView, ViewGroup parent) {

        final String childText = (String) getChild(groupPosition, childPosition);

        if (convertView == null) {
            LayoutInflater infalInflater = (LayoutInflater) this._context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = infalInflater.inflate(R.layout.list_item, null);
        }

        TextView txtListChild = (TextView) convertView
                .findViewById(R.id.lblListItem);

        txtListChild.setText(childText);
        return convertView;
    }
    
    @Override
public int getChildrenCount(int groupPosition) {
        return this._listDataChild.get(this._listDataHeader.get(groupPosition)).size();
    }
    @Override
public Object getGroup(int groupPosition) {
        return this._listDataHeader.get(groupPosition);
    }
    
    @Override
public int getGroupCount() {
        return this._listDataHeader.size();
    }
    
    @Override
public long getGroupId(int groupPosition) {
        return groupPosition;
    }
    
    @Override
public View getGroupView(int groupPosition, boolean isExpanded,
                             View convertView, ViewGroup parent) {
        String headerTitle = (String) getGroup(groupPosition);
        if (convertView == null) {
            LayoutInflater infalInflater = (LayoutInflater) this._context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = infalInflater.inflate(R.layout.list_group, null);
        }

        TextView lblListHeader = (TextView) convertView
                .findViewById(R.id.lblListHeader);
        lblListHeader.setTypeface(null, Typeface.BOLD);
        lblListHeader.setText(headerTitle);

        return convertView;
    }
    
    @Override
public boolean hasStableIds() {
        return false;
    }
    
    @Override
public boolean isChildSelectable(int groupPosition, int childPosition) {
        return true;
    }
}