Any samples please?

[vijimscse]

Right now, only groups are being displayed. not the child list.On clicking group, corresponding children list should be displayed. When I debugged, getChildrenList() is not getting called at all. It is better if shared some samples for understanding.

[AndXorr]

I think you need override @canExpand in your ViewHolder.
Example simple adapter for String(group) and String(child).
I have a worked project. If you have any questions you can ask me.

package biz.andxor.trains.adapters;

import android.content.Context;
import android.support.annotation.NonNull;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.List;
import java.util.Map;

import biz.andxor.trains.R;
import biz.andxor.trains.views.RecyclerView.ExpandableRecyclerView;

public class CabinAdapter extends ExpandableRecyclerView.ExpandableAdapter<CabinAdapter.Holder, String> {

    private Context context;
    private List<String> listGroups;
    private Map<String, List<String>> listChildren;

    public CabinAdapter(Context context, List<String> listDataHeader, Map<String, List<String>> listChildData) {
        this.context = context;
        this.listGroups = listDataHeader;
        this.listChildren = listChildData;
    }


    @NonNull
    @Override
    protected Holder onCreateExpandableViewHolder(ViewGroup parent, int viewType) {
        switch (viewType) {
            case 0:
                return new Holder(LayoutInflater.from(context).inflate(R.layout.item_group, parent, false));
            case 1:
                return new Holder(LayoutInflater.from(context).inflate(R.layout.item_list, parent, false));
            default:
                throw new IllegalArgumentException("Unknown view type ="+viewType);
        }
    }

    @Override
    protected void onBindGroupView(Holder holder, int groupPosition) {
        holder.group.setText(listGroups.get(groupPosition));
    }

    public Object getChild(int groupPosition, int childPosition) {
        return listChildren.get(listGroups.get(groupPosition)).get(childPosition);
    }

    @Override
    protected void onBindChildView(Holder holder, int groupPosition, int childPosition) {
        final String childText = (String) getChild(groupPosition, childPosition);
        holder.item.setText(childText);
    }

    @Override
    protected int getGroupCount() {
        return listGroups.size();
    }

    @Override
    protected int getChildrenCount(int groupPosition) {
        return listChildren.get(this.listGroups.get(groupPosition)).size();
    }

    @Override
    protected int getGroupViewType(int groupPosition) {
        return 0;
    }

    @Override
    protected int getChildViewType(int groupPosition, int childPosition) {
        return 1;
    }

    @Override
    public String getGroup(int groupPosition) {
        return listGroups.get(groupPosition);
    }

    public class Holder extends ExpandableRecyclerView.ExpandableViewHolder {

        private TextView group, item;

        public Holder(View itemView) {
            super(itemView);
            group = (TextView) itemView.findViewById(R.id.lblListHeader);
            item = (TextView) itemView.findViewById(R.id.lblListItem);
        }

        @Override
        protected boolean canExpand() {
            return true;
        }
    }
}