How to update the index of Bottom Navigation Bar ? - Flutter

Question

I want to update the current index of the BottomNavigation Bar by ValueNotifier or anything instead of . and I don't need to wrap the bottom bar by Scaffold , because when I did it , the home screen didn't load . And I jsut updated the current index by Push if back button pressed or WillPopScope ,but I need it pop.. to save scroll's position and updated the index . Please if you have a solution drop it here .

class AppBottomNavigation extends StatefulWidget {

  const AppBottomNavigation({Key? key}) : super(key: key);
  @override
  _AppBottomNavigationState createState() => _AppBottomNavigationState();
}
class _AppBottomNavigationState extends State<AppBottomNavigation> {
  int _selectedIndex = 0 ;
  int _pastIndex = 0 ;
  List<Widget> _screens =[
    HomeScreen(),
    Scaffold(body: Text("No widget yet")),
    Scaffold(body: Text("No widget yet")),
    Scaffold(body: Text("No widget yet")),
    UserProfile()
  ];
   
  List<dynamic> menuItems = [
    {
      'icon': 'assets/icons/home.svg',
      'label': 'Home',
    },
    {
      'icon': 'assets/icons/box.svg',
      'label': 'Delivery',
    },
    {
      'icon': 'assets/icons/chat.svg',
      'label': 'Messages',
    },
    {
      'icon': 'assets/icons/wallet.svg',
      'label': 'Wallet',
    },
    {
      'icon': 'assets/icons/profile.svg',
      'label': 'Profile',
    },
  ];

  void _onItemTapped(int index) {
      setState(() {
        _selectedIndex = index;
      });
        if (index == 4) {
        if(FirebaseAuth.instance.currentUser != null){
          Navigator.push(
                context,
                MaterialPageRoute(
                  builder: (context) => UserProfile(),
                ));
          
        }else{
          try {
            Navigator.push(
                context,
                MaterialPageRoute(
                  builder: (context) => LoginScreen(),
                ));
          } on Exception catch (e) {
            print(e);
          }

        }  
      } else {
        if(_selectedIndex != _pastIndex){
          Navigator.push(
                  context,
                  MaterialPageRoute(
                    builder: (context) => _screens[_selectedIndex],
                  ));
      }
      
      }
      setState(() {
        _pastIndex = _selectedIndex;
      });
    
  }

  @override
  Widget build(BuildContext context) {
    return BottomNavigationBar(  
      backgroundColor: Colors.white,
      showUnselectedLabels: true,
      unselectedItemColor: Colors.black87,
      elevation: 32.0,
      type: BottomNavigationBarType.fixed,
      selectedLabelStyle: TextStyle(
        height: 1.5,
        fontSize: 12,
      ),
      unselectedLabelStyle: TextStyle(
        height: 1.5,
        fontSize: 12,
      ),
      items: menuItems.map((i) {
        return BottomNavigationBarItem(
          icon: SvgPicture.asset(i['icon']),
          activeIcon: SvgPicture.asset(
            i['icon'],
            color: primaryColor,
          ),
          label: i['label'],
        );
      }).toList(),
      currentIndex: _selectedIndex,
      selectedItemColor: MyEditColor,
      onTap: _onItemTapped,
    );
  }
}

Here is the blulid Function of the HomeScreen and the call up of AppBottomNavigation class .

 @override
  Widget build(BuildContext context) {
    super.build(context);
    return Scaffold(
      bottomNavigationBar: AppBottomNavigation(),
      body: SafeArea(
        child: SingleChildScrollView(
          child: Column(

            //....