Flutter: how to show a badge in a CupertinoTabBar and update the value based on user input

Question

I have a CupertinoApp with a CupertinoTabScaffold, a CupertinoTabBar and a series of BottomNavigationBarItem(s). I managed to add a badge in one of the BottomNavigationBarItem (the basket tab). See the picture below as well as my code

class _HomeScreenState extends State<HomeScreen> {
  @override
  Widget build(BuildContext context) {
    return CupertinoTabScaffold(
      tabBar: CupertinoTabBar(
        backgroundColor: kColorPrimaryLight,
        items: [
          BottomNavigationBarItem(
            icon: Icon(CupertinoIcons.search),
            title: Text('Discover'),
          ),
          BottomNavigationBarItem(
            icon: Icon(CupertinoIcons.person_solid),
            title: Text('Account'),
          ),
          BottomNavigationBarItem(
            icon: Icon(CupertinoIcons.book_solid),
            title: Text('Stories'),
          ),
          BottomNavigationBarItem(
            icon: Badge(
                badgeContent: Text(
                  appData.basketList.length.toString(),
                  style: kDescriptionTextStyle,
                ),
                child: Icon(CupertinoIcons.shopping_cart)),
            title: Text('Basket'),
          ),
        ],
      ),

Now I would like to update that badge text based on an event which get triggered in one of the the other tab. I am storing the value of the badge in a singletons (appData.basketList) and this information is available to all my screens. Every time I trigger that event then the appData.basketList.length.toString() changes but my badge does not change. It only change if I hot reload... so here is my question: how can I update the text of my badge?

Thanks !