Shopping cart using bloc does not update cart count

I'm trying to build a simple shopping cart using bloc. It works fine but the only issue is the cart count doesn't get updated when I add/remove the item. I need to switch to the cartscreen to see the change. I set the counter to cartBloc.cart.length.toString(). What am I missing and am I using bloc correctly?

Cart Bloc

class CartBloc{

  List<ProductModel> cart = [];
  double totalCartPrice = 0;

  final _cartController = StreamController.broadcast();
  Stream get getCartStream => _cartController.stream;

  void addToCart(ProductModel product) {
    cart.add(product);
    totalCartPrice = totalCartPrice + double.parse(product.price);
    _cartController.sink.add(cart);
  }
  void removeFromCart(ProductModel product) {
    cart.remove(product);
    totalCartPrice = totalCartPrice - double.parse(product.price);
    _cartController.sink.add(cart);
  }
  void dispose() {
    _cartController?.close();
  }
}
final cartBloc = CartBloc();

Main Screen

class _MainScreenState extends State<MainScreen> {

      int _currentIndex = 0;
      PageController _pageController;
      GlobalKey bottomNavigationKey = GlobalKey();

      @override

      void initState() {
        super.initState();
        _pageController = PageController();
      }
      
      void dispose(){
        super.dispose();
        _pageController.dispose();
      }

      @override

      Widget build(BuildContext context) {
        return Scaffold(
          backgroundColor:Color(0xFF20232A),
          appBar: PreferredSize(child: Container(),preferredSize: Size.fromHeight(0.0)),
          body: SizedBox.expand(
            child: PageView(
              physics: NeverScrollableScrollPhysics(),
              controller: _pageController,
              onPageChanged: (index){
                setState(() => _currentIndex = index);
              },
              children: [
                Container(
                  child: ProductScreen()
                ),
                Container(
                  child: CartScreen()
                ),
              ],
            )
          ),
          bottomNavigationBar: Container(
            child: BottomNavyBar(
              mainAxisAlignment: MainAxisAlignment.center,
              containerHeight: 56.0,
              backgroundColor: Style.Colors.backgroundColor,
              selectedIndex: _currentIndex,
              onItemSelected: (index){
                setState(() => _currentIndex = index);
                _pageController.jumpToPage(index);
              },
              items:<BottomNavyBarItem>[
                BottomNavyBarItem(
                  textAlign: TextAlign.center,
                  activeColor: Color(0xFF010101),
                  title: Text(' PRODUCTS',style: TextStyle(
                    color:Style.Colors.mainColor,fontSize: 13.0
                  )),
                  icon: Padding(
                    padding: EdgeInsets.only(left:5.0),
                    child: Icon(
                      SimpleLineIcons.menu,
                      size:18.0,
                      color:_currentIndex == 0 ? Style.Colors.mainColor:Colors.white
                    ),
                  )
                ),
                BottomNavyBarItem(
                  textAlign: TextAlign.center,
                  activeColor: Color(0xFF010101),
                  title: Text(' CART',style: TextStyle(
                    color:Style.Colors.mainColor,fontSize: 13.0
                  )),
                  icon: Padding(
                    padding: EdgeInsets.only(left:5.0),
                    child: Badge(
                        badgeColor: Style.Colors.mainColor,
                        badgeContent: Text(cartBloc.cart.length.toString(),style: TextStyle(fontWeight: FontWeight.bold),), //not updating when select item
                        child: Icon(
                          SimpleLineIcons.basket,
                          size:18.0,
                          color:_currentIndex == 1 ? Style.Colors.mainColor:Colors.white
                        ),
                    )
                  )
                ),
              ]
            ),
          ),
        );
      }
    }