How to count "selected" items in RecyclerView, bases on checkbox status

Question

I have a RecyclerView with a checkbox component, underneath there is a list of POJO with "isSelected" attribute.

Everything work fine when no items are selected at startup.

But in some conditions, I will need to show the list with the checkbox selected at start.

So I added some logic in the bind method in the adapter.

And works fine.

But now I want to show the user the qty of lines selected!

in the fragment I'm trying to filter and count the elements in the list that area selected

     ensayoSeleccionAdapter.submitList(it.data)
     binding.btnSeleccionar.isEnabled = true
     val selected = ensayoSeleccionAdapter.currentList.filter { e -> e.isSelected }

The problem is that I only get an empty list.

I try to use:

   ensayoSeleccionAdapter.registerAdapterDataObserver(object : RecyclerView.AdapterDataObserver() {

but the result is the same.

Any idea? Thanks!