نمونه ای که خودم نوشتم با متد popscop 

import 'package:flutter/material.dart';
import 'package:nikestore/screens/home/home.dart';
import 'package:nikestore/screens/product/productScreen.dart';
import 'package:nikestore/screens/profile/profileScreen.dart';
const int homeIndex = 0;
const int product = 1;
const int profileIndex = 2;
final homeNavigatorKey = GlobalKey<NavigatorState>();
final productNavigatorKey = GlobalKey<NavigatorState>();
final profileNavigatorKey = GlobalKey<NavigatorState>();
class RootScreen extends StatefulWidget {
  const RootScreen({super.key});
  @override
  State<RootScreen> createState() => _RootScreenState();
}
class _RootScreenState extends State<RootScreen> {
  int selectedScreenIndex = homeIndex;
  late List<int> navigationStack = [homeIndex];
  // Future<bool> onWillPop() async {
  //   // If there's more than one screen in the stack, pop back to the previous one
  //   if (navigationStack.length > 1) {
  //     navigationStack.removeLast(); // Remove current screen
  //     setState(() {
  //       selectedScreenIndex = navigationStack.last; // Go to previous screen
  //     });
  //     return false; // Prevents pop
  //   }
  //   // If only one screen (home), then exit the app
  //   return true; // Allows pop
  // }
  Future<bool> onWillPop() async {
    final currentNavigator = switch (selectedScreenIndex) {
      homeIndex => homeNavigatorKey.currentState,
      product => productNavigatorKey.currentState,
      profileIndex => profileNavigatorKey.currentState,
      _ => null,
    };
    if (currentNavigator != null &&
        currentNavigator.canPop()) {
      currentNavigator.pop();
      return false;
    }
    if (navigationStack.length > 1) {
      navigationStack.removeLast();
      setState(() {
        selectedScreenIndex = navigationStack.last;
      });
      return false;
    }
    return true;
  }
  void navigateToScreen(int screenIndex) {
    setState(() {
      selectedScreenIndex = screenIndex;
      // If the screen is already in the stack, don't add it again
      if (navigationStack.contains(screenIndex)) {
        // Move it to the end to show it's the most recent
        navigationStack.remove(screenIndex);
      }
      navigationStack.add(screenIndex);
    });
  }
  @override
  Widget build(BuildContext context) {
    return PopScope(
      canPop: false, // Prevents immediate system pop when false
      onPopInvokedWithResult: (bool didPop, Object? result) async {
        // If the system already handled the pop, do nothing
        if (didPop) return;
        // Run your custom logic (e.g., show a dialog)
        final bool shouldPop = await onWillPop();
        // Manually trigger pop if user confirms
        if (shouldPop && context.mounted) {
          Navigator.of(context).pop(result);
        }
      },
      child: Scaffold(
        bottomNavigationBar: BottomNavigationBar(
            items: [
          BottomNavigationBarItem(icon: Icon(Icons.home),label: "Home"),
          BottomNavigationBarItem(icon: Icon(Icons.add_shopping_cart),label: "Cart"),
          BottomNavigationBarItem(icon: Icon(Icons.person),label: "Profile"),
        ],
        currentIndex: selectedScreenIndex,
            onTap: (index){
              navigateToScreen(index);
            },
        ),
        body: Stack(
          children: [
            Positioned.fill(
              bottom: 10,
           child:IndexedStack(
                index: selectedScreenIndex,
                children: [
                  Navigator(
                    key: homeNavigatorKey,
                    onGenerateRoute: (_) => MaterialPageRoute(
                      builder: (_) => HomeScreen(),
                    ),
                  ),
                  Navigator(
                    key: productNavigatorKey,
                    onGenerateRoute: (_) => MaterialPageRoute(
                      builder: (_) => ProductScreen(),
                    ),
                  ),
                  Navigator(
                    key: productNavigatorKey,
                    onGenerateRoute: (_) => MaterialPageRoute(
                      builder: (_) => ProfileScreen(),
                    ),
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}