一、概念

一种用于垂直滚动展示两级列表的视图，和ListView的不同之处就是它可以展示两级列表，分组可以单独展开显示子选项，这些选项的数据是通过ExpandableListAdapter关联的。ExpandableListAdapter和ListView使用的BaseAdapter差不多，都是用来给View加载布局文件、绑定数据的。

二、使用

//数据
public String[] groupStrings = {"西游记", "水浒传", "三国演义", "红楼梦"};
public String[][] childStrings = {
            {"唐三藏", "孙悟空", "猪八戒", "沙和尚"},
            {"宋江", "林冲", "李逵", "鲁智深"},
            {"曹操", "刘备", "孙权", "诸葛亮", "周瑜"},
            {"贾宝玉", "林黛玉", "薛宝钗", "王熙凤"}
    };

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

//分组的视图和子选项的视图
<TextView
    android:id="@+id/label_expand_group"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center_vertical"
    android:background="@android:color/holo_blue_light"
    android:paddingLeft="20dp"
    android:textColor="@android:color/white"
    android:textSize="20sp" />

//自定义适配器，继承BaseExpandableListAdapter
    //        获取分组的个数
    @Override
    public int getGroupCount() {
        return groupStrings.length;
    }

    //        获取指定分组中的子选项的个数
    @Override
    public int getChildrenCount(int groupPosition) {
        return childStrings[groupPosition].length;
    }

    //        获取指定的分组数据
    @Override
    public Object getGroup(int groupPosition) {
        return groupStrings[groupPosition];
    }

    //        获取指定分组中的指定子选项数据
    @Override
    public Object getChild(int groupPosition, int childPosition) {
        return childStrings[groupPosition][childPosition];
    }

    //        获取指定分组的ID, 这个ID必须是唯一的
    @Override
    public long getGroupId(int groupPosition) {
        return groupPosition;
    }

    //        获取子选项的ID, 这个ID必须是唯一的
    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return childPosition;
    }

    //        分组和子选项是否持有稳定的ID, 就是说底层数据的改变会不会影响到它们。
    @Override
    public boolean hasStableIds() {
        return true;
    }
    //        获取显示指定分组的视图
    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
        GroupViewHolder groupViewHolder;
        if (convertView == null) {
            convertView = LayoutInflater.from(MainActivity.this).inflate(R.layout.item_expand_group, parent, false);
            groupViewHolder = new GroupViewHolder();
            groupViewHolder.tvTitle = (TextView) convertView.findViewById(R.id.label_expand_group);
            convertView.setTag(groupViewHolder);
        } else {
            groupViewHolder = (GroupViewHolder) convertView.getTag();
        }
        groupViewHolder.tvTitle.setText(groupStrings[groupPosition]);
        return convertView;
    }

    //        获取显示指定分组中的指定子选项的视图
    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
        ChildViewHolder childViewHolder;
        if (convertView == null) {
            convertView = LayoutInflater.from(MainActivity.this).inflate(R.layout.item_expand_child, parent, false);
            childViewHolder = new ChildViewHolder();
            childViewHolder.tvTitle = (TextView) convertView.findViewById(R.id.label_expand_child);
            convertView.setTag(childViewHolder);
        } else {
            childViewHolder = (ChildViewHolder) convertView.getTag();
        }
        childViewHolder.tvTitle.setText(childStrings[groupPosition][childPosition]);
        return convertView;
    }

    //        指定位置上的子元素是否可选中
    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) {
        return true;
    } 

    static class GroupViewHolder {
        TextView tvTitle;
    }

    static class ChildViewHolder {
        TextView tvTitle;
    }

//设置适配器
expandableListView.setAdapter(new MyExpandableListAdapter());

//设置监听器
//        设置分组项的点击监听事件
expandableListView.setOnGroupClickListener(new ExpandableListView.OnGroupClickListener() {
    @Override
    public boolean onGroupClick(ExpandableListView expandableListView, View view, int i, long l) {
        Toast.makeText(getApplicationContext(), groupStrings[i], Toast.LENGTH_SHORT).show();
        // 请务必返回 false，否则分组不会展开
        return false;
    }
//        设置子选项点击监听事件
expandableListView.setOnChildClickListener(new ExpandableListView.OnChildClickListener() {
    @Override
    public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) {
        Toast.makeText(getApplicationContext(), childStrings[groupPosition][childPosition], Toast.LENGTHshow();
        return true;
    }
});