flutter ExpansionTile 层级菜单的实现

 @override Widget build(BuildContext context) {  return ListTile(   title: _buildItem(widget.bean),  ); } Widget _buildItem(NameBean bean){  if(bean.children.isEmpty){   return ListTile(    title: Text(bean.name),    onTap: (){     _showSeletedName(bean.name);    },   );  }  return ExpansionTile(   key: PageStorageKey<NameBean>(bean),   title: Text(bean.name),   children: bean.children.map<Widget>(_buildItem).toList(),   leading: CircleAvatar(    backgroundColor: Colors.green,    child: Text(bean.name.substring(0,1),style: TextStyle(color: Colors.white),),   ),  ); }

/// A single-line [ListTile] with a trailing button that expands or collapses/// the tile to reveal or hide the [children].////// This widget is typically used with [ListView] to create an/// "expand / collapse" list entry. When used with scrolling widgets like/// [ListView], a unique [PageStorageKey] must be specified to enable the/// [ExpansionTile] to save and restore its expanded state when it is scrolled/// in and out of view.////// See also:////// * [ListTile], useful for creating expansion tile [children] when the///  expansion tile represents a sublist./// * The "Expand/collapse" section of///  <https://material.io/guidelines/components/lists-controls.html>.class ExpansionTile extends StatefulWidget {