通常你会有一个在每个页面上都有自己的AppBar的Scaffold，但是为什么go_router需要它呢？为什么你不能有一个单独的带有AppBar的Scaffold，让它来处理导航。
在本例中，转到SecondScreen不会更新AppBar并显示后退按钮。
为什么这是不可能的？

import 'package:flutter/material.dart';
import 'package:go_router/go_router.dart';

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

final GoRouter _router = GoRouter(
  routes: <RouteBase>[
    ShellRoute(
      builder: (context, state, child) {
        return Scaffold(
          body: child,
          appBar: AppBar(
            title: const Text('Test'),
          ),
        );
      },
      routes: [
        GoRoute(
          path: '/',
          pageBuilder: ((context, state) => const NoTransitionPage(
                child: HomeScreen(),
              )),
          routes: [
            GoRoute(
              path: 'second',
              pageBuilder: ((context, state) => const NoTransitionPage(
                    child: SecondScreen(),
                  )),
            ),
          ],
        ),
      ],
    ),
  ],
);

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp.router(
      routerConfig: _router,
    );
  }
}

class HomeScreen extends StatelessWidget {
  const HomeScreen({super.key});

  @override
  Widget build(BuildContext context) {
    return Center(
      child: ElevatedButton(
        onPressed: () => context.go('/second'),
        child: const Text('Go to the Second screen'),
      ),
    );
  }
}

class SecondScreen extends StatelessWidget {
  const SecondScreen({super.key});

  @override
  Widget build(BuildContext context) {
    return const Center(
      child: Text('Second screen'),
    );
  }
}