flutter_bug_quick_back_button.dart

import 'package:flutter/material.dart';

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

class MainApp extends StatelessWidget {
  final RouterDelegate<AppState> _routerDelegate = MainRouterDelegate();

  MainApp({super.key});
  @override
  Widget build(BuildContext context) =>
    MaterialApp.router(
      routerDelegate: _routerDelegate,
      backButtonDispatcher: RootBackButtonDispatcher(),
    );
}

class MainRouterDelegate extends RouterDelegate<AppState>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<AppState> {

  @override
  final GlobalKey<NavigatorState> navigatorKey;
  
  MainRouterDelegate() : navigatorKey = GlobalKey<NavigatorState>();

  final AppState appState = AppState();
  
  @override
  Widget build(BuildContext context) => Navigator(
      key: navigatorKey,
      pages: [
        MaterialPage(
          child: MainScreen(
            key: const ValueKey("mainScreen"),
            text: "My Page",
            appState: appState,
          )
        ),
        const MaterialPage(child: InnerScreen(text: "Inner screen")) 
      ],
      onPopPage: (route, result) {
        print('MainRouter#onPopPage');

        if (!route.didPop(result)) {
          return false;
        }

        return true;
      },
    );

  @override
  Future<void> setNewRoutePath(AppState configuration) async {
  }
}

class MainScreen extends StatefulWidget {
  MainScreen({super.key, required this.text, required this.appState}): _innerRouterDelegate = InnerRouterDelegate();

  final String text;
  final AppState appState;
  final RouterDelegate<AppState> _innerRouterDelegate;

  @override
  State<MainScreen> createState() => _MainScreenState();
}

class _MainScreenState extends State<MainScreen> {

  @override
  Widget build(BuildContext context) => Scaffold(
      body: Router(
        routerDelegate: widget._innerRouterDelegate,
      ),
    );
}

class InnerRouterDelegate extends RouterDelegate<AppState>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<AppState> {

  @override
  final GlobalKey<NavigatorState> navigatorKey;

  InnerRouterDelegate() : navigatorKey = GlobalKey<NavigatorState>(); 
  
  @override
  Widget build(BuildContext context) => Navigator(
      key: navigatorKey,
      pages: const [
        MaterialPage(
          child: InnerScreen(
            key: ValueKey("innerScreen"),
            text: "Main screen",
          )
        ),
      ],
      onPopPage: (route, result) {
        print('InnerRouter#onPopPage');

        if (!route.didPop(result)) {
          return false;
        }

        return true;
      },
    );

  @override
  Future<void> setNewRoutePath(AppState configuration) async {
  }
}

class AppState extends ChangeNotifier {
}

class InnerScreen extends StatelessWidget {
  const InnerScreen({super.key, required this.text});

  final String text;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Center(
        child: Column(
          children: [
            Text(text),
          ],
        ),
      ),
    );
  }
}