Updating PopScope based on inner Navigator

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Builder(
        builder: (context) {
          return Scaffold(
            appBar: AppBar(title: Text('Home')),
            body: Center(
              child: ElevatedButton(
                onPressed: () => Navigator.of(context).push(
                  MaterialPageRoute(
                    builder: (_) => NestedNavScreen(),
                  ),
                ),
                child: Text('Open top level'),
              ),
            ),
          );
        },
      ),
    );
  }
}

class NestedNavScreen extends StatefulWidget {
  @override
  State<NestedNavScreen> createState() => _NestedNavScreenState();
}

class _NestedNavScreenState extends State<NestedNavScreen> {
  final _navigatorKey = GlobalKey<NavigatorState>();

  Route _onGenerateRoute(RouteSettings settings) {
    final routeName = settings.name!;
    final routeIndex = int.parse(routeName);
    return MaterialPageRoute(
      builder: (_) => NestedPage(index: routeIndex),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Nested Nav screen')),
      body: PopScope(
        // Don't pop if the inner nav can pop
        //
        // ------
        // We want PopScope to rebuild when the inner nav changes, so `canPop` has a new value.
        // It might have the wrong value when the Android back button is used.
        // ------
        canPop: _navigatorKey.currentState?.canPop() ?? true,
        onPopInvokedWithResult: (didPop, _) {
          // No need to pop the inner nav
          if (didPop) return;
          // Pop the inner nav
          _navigatorKey.currentState?.pop();
        },
        child: Navigator(
          key: _navigatorKey,
          initialRoute: '1',
          onGenerateRoute: _onGenerateRoute,
        ),
      ),
    );
  }
}

class NestedPage extends StatelessWidget {
  NestedPage({required this.index});

  final int index;

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        children: [
          Text('Nested page: $index'),
          Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              if (Navigator.of(context).canPop())
                ElevatedButton(
                  onPressed: () => Navigator.of(context).pop(),
                  child: Text('Go back'),
                ),
              ElevatedButton(
                onPressed: () =>
                    Navigator.of(context).pushNamed('${index + 1}'),
                child: Text('Open next'),
              ),
            ],
          ),
        ],
      ),
    );
  }
}