flutterドロップダウンメニューは記録のみ

どちらも転載してきました
第1種の転入https://blog.csdn.net/weixin_33835103/article/details/88490202 main.dart

import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return new MaterialApp(
      title: "flutter demo",
      theme: new ThemeData.dark(),
      home: _home(),
    );
  }
}
class _home extends StatefulWidget {
  @override
  State createState() {
    // TODO: implement createState
    return _homeState();
  }
}
class _homeState extends State<_home> {
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return new Scaffold(
      appBar: new AppBar(
        title: new Text("title"),
      ),
      body: new Center(
        child: ExpansionTile(
            title: Text("title"),
            leading: Icon(Icons.favorite,color: Colors.white,),
            backgroundColor: Colors.lightBlue,
            initiallyExpanded: false,//      
            children: [
              ListTile(
                title: Text("ListTile"),
                leading: Icon(Icons.favorite_border,color: Colors.white,),
              ),
            ],
        ),
      ),
    );
  }
}

第2の転入https://flutterchina.club/catalog/samples/expansion-tile-sample/
main.dart  

import 'package:flutter/material.dart';

class ExpansionTileSample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('ExpansionTile'),
        ),
        body: ListView.builder(
          itemBuilder: (BuildContext context, int index) => EntryItem(data[index]),
          itemCount: data.length,
        ),
      ),
    );
  }
}

// One entry in the multilevel list displayed by this app.
class Entry {
  Entry(this.title, [this.children = const []]);
  final String title;
  final List children;
}

// The entire multilevel list displayed by this app.
final List data = [
  Entry('Chapter A',
    [
      Entry('Section A0',
        [
          Entry('Item A0.1'),
          Entry('Item A0.2'),
          Entry('Item A0.3'),
        ],
      ),
      Entry('Section A1'),
      Entry('Section A2'),
    ],
  ),
  Entry('Chapter B',
    [
      Entry('Section B0'),
      Entry('Section B1'),
    ],
  ),
  Entry('Chapter C',
    [
      Entry('Section C0'),
      Entry('Section C1'),
      Entry('Section C2',
        [
          Entry('Item C2.0'),
          Entry('Item C2.1'),
          Entry('Item C2.2'),
          Entry('Item C2.3'),
        ],
      ),
    ],
  ),
];

// Displays one Entry. If the entry has children then it's displayed
// with an ExpansionTile.
class EntryItem extends StatelessWidget {
  const EntryItem(this.entry);

  final Entry entry;

  Widget _buildTiles(Entry root) {
    if (root.children.isEmpty)
      return ListTile(title: Text(root.title));
    return ExpansionTile(
      key: PageStorageKey(root),
      title: Text(root.title),
      children: root.children.map(_buildTiles).toList(),
    );
  }

  @override
  Widget build(BuildContext context) {
    return _buildTiles(entry);
  }
}

void main() {
  runApp(ExpansionTileSample());
}

/*
Sample Catalog
Title: ExpansionTile
Summary: An ExpansionTile for building nested lists, with two or more levels.
Description:
This app displays hierarchical data with ExpansionTiles. Tapping a tile
expands or collapses the view of its children. When a tile is collapsed
its children are disposed so that the widget footprint of the list only
reflects what's visible.
When displayed within a scrollable that creates its list items lazily,
like a scrollable list created with `ListView.builder()`, ExpansionTiles
can be quite efficient, particularly for material design "expand/collapse"
lists.
Classes: ExpansionTile, ListView
Sample: ExpansionTileSample
See also:
  - The "expand/collapse" part of the material design specification:
    
*/