FastScroll position is incorrect after restoring from savedState whereas RecyclerView state is correct

[yaroslav-shlapak]

FlexibleAdapeter 5.1.0, Android 9.0, Pixel 1

After restoring state of RecyclerView and FlexibleAdapter, FastScroll position is wrong or not visible. On user scrolling FastScroll handle jumps to the correct position.

This issue is visible on example apk on configuration changes on any Fragment with FastScroll.

My particular case:

1. Save state using Evernote state lib:

@Parcelize
data class RecyclerSavedState(
        val position: Int,
        val state: Parcelable?,
        val adapterState: Bundle?
) : Parcelable

    @State
    var savedState: RecyclerSavedState? = null

    override fun onPause() {
        super.onPause()
        val state = Bundle()
        adapter?.onSaveInstanceState(state)
        savedState = RecyclerSavedState(
                adapter?.stickyPosition ?: 0,
                alertsRecycler?.layoutManager?.onSaveInstanceState(),
                state
        )
    }

2. Observe items in Fragment:

   
   override fun onActivityCreated(savedInstanceState: Bundle?) {
       super.onActivityCreated(savedInstanceState)
       viewModel.items.observe(viewLifecycleOwner, Observer { newAlertList ->
           newAlertList?.let { list ->
                   adapter?.submitList(list, savedState)
           })
   }

3. FlexibleAdapter extension:

class RecyclerAdapter( items: List<AbstractFlexibleItem<>>, listeners: Any ) : FlexibleAdapter<AbstractFlexibleItem<>>(items, listeners, true) { private var recyclerSavedState: RecyclerSavedState? = null

fun submitList(items: List<ItemHolder>?, recyclerSavedState: RecyclerSavedState?) {
    this.recyclerSavedState = recyclerSavedState
    this.postUpdate = postUpdate
    items?.let {
        updateDataSet(items, false)
    }
}

override fun onPostUpdate() {
    super.onPostUpdate()
    updateState()
}

private fun updateState() {
    recyclerSavedState?.let {
        recyclerView.layoutManager?.onRestoreInstanceState(it.state)
        onRestoreInstanceState(it.adapterState)
    } ?: kotlin.run {
        recyclerView?.scrollToPosition(0)
    }
}

}

Is there any way to initialize FastScroll with correct position?