ExpandableListView 是 Android 中的一個組件，它可以用來實現樹形結構的數據展示

1. 首先，在 res/layout 目錄下創建一個布局文件 list_item.xml，用于顯示每個列表項：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:padding="8dp">

   <TextView
        android:id="@+id/tv_item"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="16sp" />

</LinearLayout>

2. 創建一個 Java 類 MyExpandableListAdapter，繼承自 BaseExpandableListAdapter：

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.List;
import java.util.Map;

public class MyExpandableListAdapter extends BaseExpandableListAdapter {

    private Context context;
    private List<String> groupList;
    private Map<String, List<String>> childList;

    public MyExpandableListAdapter(Context context, List<String> groupList, Map<String, List<String>> childList) {
        this.context = context;
        this.groupList = groupList;
        this.childList = childList;
    }

    @Override
    public int getGroupCount() {
        return groupList.size();
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        return childList.get(groupList.get(groupPosition)).size();
    }

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

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

    @Override
    public long getGroupId(int groupPosition) {
        return groupPosition;
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return childPosition;
    }

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

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(R.layout.list_item, parent, false);
        }
        TextView tvItem = convertView.findViewById(R.id.tv_item);
        tvItem.setText(groupList.get(groupPosition));
        return convertView;
    }

    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(R.layout.list_item, parent, false);
        }
        TextView tvItem = convertView.findViewById(R.id.tv_item);
        tvItem.setText(childList.get(groupList.get(groupPosition)).get(childPosition));
        return convertView;
    }

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

3. 在你的 Activity 或 Fragment 中，初始化 ExpandableListView 并設置適配器：

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

import androidx.appcompat.app.AppCompatActivity;

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

public class MainActivity extends AppCompatActivity {

    private ExpandableListView expandableListView;
    private MyExpandableListAdapter adapter;

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

        expandableListView = findViewById(R.id.expandableListView);

        // 初始化數據
        List<String> groupList = new ArrayList<>();
        groupList.add("Group 1");
        groupList.add("Group 2");
        groupList.add("Group 3");

        Map<String, List<String>> childList = new HashMap<>();
        List<String> childList1 = new ArrayList<>();
        childList1.add("Child 1-1");
        childList1.add("Child 1-2");
        childList.put("Group 1", childList1);

        List<String> childList2 = new ArrayList<>();
        childList2.add("Child 2-1");
        childList2.add("Child 2-2");
        childList2.add("Child 2-3");
        childList.put("Group 2", childList2);

        List<String> childList3 = new ArrayList<>();
        childList3.add("Child 3-1");
        childList.put("Group 3", childList3);

        // 設置適配器
        adapter = new MyExpandableListAdapter(this, groupList, childList);
        expandableListView.setAdapter(adapter);
    }
}

4. 在 res/layout/activity_main.xml 中添加 ExpandableListView：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

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

</LinearLayout>

現在運行應用程序，你將看到一個樹形結構的列表。點擊父節點時，子節點將展開或收起。