<ExpandableListView
    android:id="@+id/expandableListView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

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

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

public class MyExpandableListAdapter extends BaseExpandableListAdapter {
    private Context context;
    private List<String> listDataHeader; // 标头列表
    private HashMap<String, List<String>> listDataChild; // 子项数据

    public MyExpandableListAdapter(Context context, List<String> listDataHeader,
                                   HashMap<String, List<String>> listDataChild) {
        this.context = context;
        this.listDataHeader = listDataHeader;
        this.listDataChild = listDataChild;
    }

    @Override
    public Object getChild(int groupPosition, int childPosition) {
        return listDataChild.get(listDataHeader.get(groupPosition)).get(childPosition);
    }

    @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 inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.list_item, null);
        }

        TextView txtListChild = convertView.findViewById(R.id.lblListItem);
        txtListChild.setText(childText);
        return convertView;
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        return listDataChild.get(listDataHeader.get(groupPosition)).size();
    }

    @Override
    public Object getGroup(int groupPosition) {
        return listDataHeader.get(groupPosition);
    }

    @Override
    public int getGroupCount() {
        return 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 inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.list_group, null);
        }

        TextView lblListHeader = convertView.findViewById(R.id.lblListHeader);
        lblListHeader.setText(headerTitle);

        return convertView;
    }

    @Override
    public boolean hasStableIds() {
        return false;
    }

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

import android.app.Activity;
import android.os.Bundle;
import android.widget.ExpandableListView;

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

public class MainActivity extends Activity {

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

        ExpandableListView expandableListView = findViewById(R.id.expandableListView);

        // 准备数据
        List<String> listDataHeader = new ArrayList<>();
        HashMap<String, List<String>> listDataChild = new HashMap<>();

        // 添加组数据
        listDataHeader.add("Group 1");
        listDataHeader.add("Group 2");

        // 添加子项数据
        List<String> group1Items = new ArrayList<>();
        group1Items.add("Item 1.1");
        group1Items.add("Item 1.2");

        List<String> group2Items = new ArrayList<>();
        group2Items.add("Item 2.1");
        group2Items.add("Item 2.2");

        listDataChild.put(listDataHeader.get(0), group1Items);
        listDataChild.put(listDataHeader.get(1), group2Items);

        // 创建适配器
        MyExpandableListAdapter listAdapter = new MyExpandableListAdapter(this, listDataHeader, listDataChild);

        // 设置适配器
        expandableListView.setAdapter(listAdapter);
    }
}