MainActivity.java

package com.demo.farooq.sublistlistview;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ExpandableListView;
import android.widget.ExpandableListView.OnGroupClickListener;
import android.widget.ExpandableListView.OnGroupExpandListener;
import android.widget.Toast;

import com.demo.farooq.sublistlistview.ExpandableListAdapter;

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

import static android.widget.ExpandableListView.*;

/**
 * Created by farooq on 1/4/2017.
 */

public class MainActivity extends AppCompatActivity {

    private static ExpandableListView expandableListView;
    private static ExpandableListAdapter adapter;
    HashMap<String, List<String>> hashMap;
    ArrayList<String> header;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        expandableListView = (ExpandableListView) findViewById(R.id.simple_expandable_listview);
        // Setting group indicator null for custom indicator
        expandableListView.setGroupIndicator(null);

        setItems();

        adapter = new ExpandableListAdapter(MainActivity.this, header, hashMap);
        // Setting adpater for expandablelistview
        expandableListView.setAdapter(adapter);

        /*
        You can add listeners for the item clicks
         */
        expandableListView.setOnGroupClickListener(new OnGroupClickListener() {

            @Override
            public boolean onGroupClick(ExpandableListView parent, View v,
                                        int groupPosition, long id) {
                return false;
            }
        });

        // Listview Group expanded listener
        expandableListView.setOnGroupExpandListener(new OnGroupExpandListener() {

            @Override
            public void onGroupExpand(int groupPosition) {
                Toast.makeText(getApplicationContext(),
                        header.get(groupPosition) + " Expanded",
                        Toast.LENGTH_SHORT).show();
            }
        });

        // Listview Group collasped listener
        expandableListView.setOnGroupCollapseListener(new OnGroupCollapseListener() {

            @Override
            public void onGroupCollapse(int groupPosition) {
                Toast.makeText(getApplicationContext(),
                        header.get(groupPosition) + " Collapsed",
                        Toast.LENGTH_SHORT).show();

            }
        });

        // Listview on child click listener
        expandableListView.setOnChildClickListener(new OnChildClickListener() {

            @Override
            public boolean onChildClick(ExpandableListView parent, View v,
                                        int groupPosition, int childPosition, long id) {

                Toast.makeText(
                        getApplicationContext(),
                        header.get(groupPosition)
                                + " : "
                                + hashMap.get(
                                header.get(groupPosition)).get(
                                childPosition), Toast.LENGTH_SHORT)
                        .show();
                return false;
            }
        });
    }


    // Setting headers and childs to expandable listview
    void setItems() {

        // Array list for header
        header = new ArrayList<String>();

        // Array list for child items
        List<String> child1 = new ArrayList<String>();
        List<String> child2 = new ArrayList<String>();
        List<String> child3 = new ArrayList<String>();
        List<String> child4 = new ArrayList<String>();

        // Hash map for both header and child
        hashMap = new HashMap<String, List<String>>();

        // Adding headers to list
        for (int i = 1; i < 5; i++) {
            header.add("Group " + i);
        }
        // Adding child data
        for (int i = 1; i < 5; i++) {
            child1.add("Child" + i);
        }
        // Adding child data
        for (int i = 1; i < 5; i++) {
            child2.add("Child" + i);
        }
        // Adding child data
        for (int i = 1; i < 6; i++) {
            child3.add("Child" + i);
        }
        // Adding child data
        for (int i = 1; i < 7; i++) {
            child4.add("Child" + i);
        }

        // Adding header and childs to hash map
        hashMap.put(header.get(0), child1);
        hashMap.put(header.get(1), child2);
        hashMap.put(header.get(2), child3);
        hashMap.put(header.get(3), child4);

    }
}