content: import 'package:flutter/material.dart';
  
  void main() => runApp(MyApp());
  
  class MyApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
      return MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: MyHomePage(title: 'Flutter Demo Home Page'),
      );
    }
  }
  
  class MyHomePage extends StatefulWidget {
    MyHomePage({Key key, this.title}) : super(key: key);
    final String title;
  
    @override
    _MyHomePageState createState() => _MyHomePageState();
  }
  
  class _MyHomePageState extends State<MyHomePage> {
    final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
  
    Widget build(BuildContext context) {
      return Scaffold(
        key: _scaffoldKey,
        body: Center(
          child: Text(
            'SnackBarのテスト',
            style: Theme.of(context).textTheme.display1,
          ),
        ),
        floatingActionButton: Builder(
          builder: (contextOfBuilder) {
            return FloatingActionButton(
              onPressed: () {
                _scaffoldKey.currentState.showSnackBar(SnackBar(content: Text('Key')));
                Scaffold.of(contextOfBuilder).showSnackBar(SnackBar(content: Text('Builder')));
                //Scaffold.of(context).showSnackBar(SnackBar(content: Text('Builder'))); // これはエラー
              },
              child: Icon(Icons.add),
            );
          },
        ),
      );
    }
  }
  