ExpandableListView :就是一种用于垂直滚动展示二级列表的视图，组可以单独展开。这些数据是通过ExpandableListView关联的。
一、使用
1.定义布局文件

    <ExpandbaleListView
            android:id="@id/expand_lv"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>

2.定义要显示的数据

  //group数据
  private ArrayList<String> GroutList;
//item数据
private ArrayList<ArrayList<String>> ItemSet;
private void initData(){
    GropList= new ArrayList<>();
    GroupList .add("家人")；
    GroupList.add("朋友")；
    GroupList.add("同事")；
}
ItemSet= new ArrayList<>();
ArrayList<String> People=new ArrayList<>();
people.add(哥哥)；
people.add(姐姐)；
people.add(弟弟)；
ArrayList<String> friend= new ArrayList<>()；
friend.add(小红)；
friend.add(小宝)；
friend.add(晓晓)；
ArrayList<String> colleagues=new ArrayList<>();
colleague.add(张三);
colleague.add(李四);
colleague.add(王五);

3.定义组视图和子选项的视图组视图

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="50dp">
<TextView
    android:layout_centerVertical="true"   
    android:layout_marginLeft="50dp"  
    android:id="@+id/tv_group"
    android:textSize="18sp"
    android:text="name"  
    android:layout_width="wrap_content"    
    android:layout_height="wrap_content" />
<TextView
   android:layout_centerVertical="true"
   android:layout_alignParentRight="true"
   android:layout_marginRight="10dp"
  android:text="4/18"
  android:textSize="16sp"
  android:layout_width="wrap_content"
 android:layout_height="wrap_content" />
 </RelativeLayout>

子视图

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_heigth="wrap_content"
  android:layout_centerVertaical="true"
  android:padding="8dp"
 <ImageView
    android:layout_marginLeft="40dp"
    android:src="@mipmap/ic_launcher"
    android:layout_width="40dp"
    android:layout_height="40dp" />
 <LinearLayout
    android:layout_marginLeft="12dp"
    android:orientation="vertical"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">
    <TextView
        android:id="@+id/tv_name"
        android:text="@string/app_name"
        android:textSize="16sp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <TextView
        android:text="@string/app_name"
        android:textSize="16sp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>
</LinearLayout>

4.自定义适配器，需要继承 BaseExpandableListAdapter 抽象类，重写相关的方法

  public class MyAdapter extends BaseExpandableListAdapter{
  private Context context;
  private ArrayList<String> group;
  private ArrayList<ArrayList<String>> ItemList;
  private final LayoutInflater inflater;
   public MyAdapter(Context context, ArrayList<String> group, ArrayList<ArrayList<String>> itemList){   
   this.context = context;
    this.group = group;
    this.ItemList = itemList;
    Inflater = LayoutInflater.from(context);
}
//父项的个数
  @Override
    public int getGroupCount() {
          return group.size();
}
//某个父项的子项的个数
 @Override
public int getChildrenCount(int groupPosition) {
    return ItemList.get(groupPosition).size();
}
//获得某个父项
  @Override
public Object getGroup(int groupPosition) {
    return group.get(groupPosition);
}
//获得某个子项
 @Override
public Object getChild(int groupPosition, int childPosition) {
    return ItemList.get(groupPosition).get(childPosition);
}
//父项的Id
 @Override
    public long getGroupId(int groupPosition){
           return groupPosition;
    }
 //子项的id
@Override
public long getChildId(int groupPosition, int childPosition) {
    return childPosition;
}
 @Override
public boolean hasStableIds() {
    return false;
}
//获取父项的view
 @Override
public View getGroupView(int    
 groupPosition, boolean isExpanded, View  
 convertView, ViewGroup parent) {
           if (convertView == null){
        convertView = Inflater.inflate(R.layout.item_group,parent,false);  }
   String group = group.get(groupPosition);
    TextView tvgroup = (TextView) convertView.findViewById(R.id.tv_group);
    tvgroup.setText(group);
    return convertView;
}
  //获取子项的view
@Override
public View getChildView(int groupPosition,       int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
    final String child = ItemList.get(groupPosition).get(childPosition);
    if (convertView == null){
        convertView = Inflater.inflate(R.layout.item_item,parent,false);
    }
    TextView tvChild = (TextView)convertView.findViewById(R.id.tv_name);
    tvChild.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
  Toast.makeText(mContext,child,Toast.LENGTH_SHORT).show();
        }
    });
   tvChild.setText(child);
    return convertView;
}
//子项是否可选中,如果要设置子项的点击事件,需要返回true
@Override
public boolean isChildSelectable(int groupPosition, int childPosition) {
    return true;
    }
}   

5.为 ExpandableListView 设置适配器

    MyAdapter adapter = new MyAdapter(this, groupList, ItemSet);  
    mExpandableListView.setAdapter(adapter);