Answer by Code on the Rocks for putting side menu and bottom navigation bar in same flutter app

The ListTiles in your drawer can set the _pageIndex to 5, 6, and 7 but there are only 5 items in your BottomNavigationBar (max valid index is 4).

I would suggest separating the logic of the drawer ListTiles from the BottomNavigationBar. In other words, don't let the drawer update the page index. Instead, tapping on a tile in the drawer should navigate to a new page.

You can reference this page to learn how navigation works in Flutter: https://docs.flutter.dev/cookbook/navigation/navigation-basics

ListTile(                    title: const Text('Add User'),                    onTap: () {                      // Close the drawer                      Navigator.pop(context);                      // Navigate to new page                      Navigator.push(                        context,                        MaterialPageRoute(builder: (context) =>                         const SecondRoute()),                       );                    },                  ),