navigation_drawer_test.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: HomeScreen(),
    );
  }
}

class HomeScreen extends StatelessWidget {
  final navigatorKey = GlobalKey<NavigatorState>();
  final title = ValueNotifier<String>("A");
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: ValueListenableBuilder<String>(
          valueListenable: title,
          builder: (_, title, __) {
            return Text(title);
          },
        ),
      ),
      drawer: Drawer(
        child: ListView(
          children: [
            DrawerHeader(child: Text("Menu")),
            ListTile(
              title: Text("Go to A"),
              onTap: () {
                // Scaffold の乗ってる navigator に対して pop して Drawer を閉じる
                Navigator.of(context).pop();
                // body の navigator に push してページ切り替え
                navigatorKey.currentState.pushNamed("a");
              }
            ),
            ListTile(
              title: Text("Go to B"),
              onTap: () {
                Navigator.of(context).pop();
                navigatorKey.currentState.pushNamed("b");
              }
            ),
          ],
        ),
      ),
      body: Navigator(
        key: navigatorKey,
        initialRoute: "a",
        onGenerateRoute: (settings) {
          final builders = <String, WidgetBuilder>{
            "a": (_) => PageA(),
            "b": (_) => PageB(),
          };
          title.value = <String, String>{
            "a": "Page A",
            "b": "Page B",
          }[settings.name];
          return MaterialPageRoute<void>(builder: builders[settings.name]);
        },
      )
    );
  }
}

class PageA extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(child: Text("A"));
  }
}

class PageB extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(child: Text("B"));
  }
}