Flutter count currently visible items of a List View

I want to show the counter on the List View that will show currently visible items of the list view / total items in the list view.

Suppose that I have 15 items in the list that I have allocated to the list view, and the items on the screen that are visible are 4/15. 4 items are those which the visible on the screen.

And when I scroll as next items get visible, the counter should be incremented and show the currentlyVisibleItems/totalItems.

I am trying like:

ScrollController scrollController;
final itemSize = 15;

scrollController = ScrollController();
scrollController.addListener(_scrollListener);

int scrolledIndex=0;
  void _scrollListener() {
    scrolledIndex = (scrollController.offset / itemSize).round() + 1;
    debugPrint("ad78798h2:::"+scrolledIndex.toString()+"/"+"15");
  }

and my list view is:

          ListView.builder(
            controller: controller.scrollController,
            shrinkWrap: true,
            scrollDirection: Axis.horizontal,
            itemCount: controller.calculateInstallmentsChipsHelperModel.length,
            itemBuilder: (BuildContext context, int index) {
              return getListViewChildItems(context, index);
            },
          ),

I simple want to show the counter for the currently visible items above the listview!

Thanks in advance