How to properly use RecycledViewPool on a multi view adapter with nested RecyclerViews?

Question

My app context so you can understand my question:

I am currently coding a very complex application with a huge dashboard that contains a huge list of nested RecyclerViews (both horizontal and vertical). I know that the vertical RV inside a vertical RV is a bad practice but unfortunately here the management and client request is stronger than our advices and they really want it implemented. How did we get to vertical RVs in vertical RV? Our backend offers basically an arrayList of groups that need to be rendered inside our dashboard. Basically a server-driven-ui. These groups contain all sorts of different designs, vertical sub-lists, horizontal sub-lists etc. I have managed to build a prototype for this DashBoard adapter so far and now I want to dive deeper inside the performance optimizations.

Things I have tried to improve performance:

I have implemented DiffUtil to make the dashboard update more efficiently on a data refresh. I have set the adapter to have stableIDs using and unique hash that every group has. I have created flat UI with constraintLayout with absolute minimum of layouts possible. I have used data binding that was proved to actually improve the performance just a little, not only better clean code. I am not doing absolutely any data processing in the adapter or viewHolders, the entire data flow comes with a final shape from higher data layers. I have set linearLayoutManager.initialPrefetchItemCount = x on every nested RVs where x is the number of items rendered on screen before any scroll.

Then I came across the RecycledViewPool. I have seen some examples of people increasing the performance of the lists with this trick. Basically they get the recyclerViewPool of the parent big adapter and they set it on the nested RVs. I have implemented this as well and my big problem is that now all my nested items get completely mixed up.

Instead of having three horizontal RVs like this:

now I have them all mixed up like this:

Here is my recycledViewPool implementation:

class GlobalAdapter : RecyclerView.Adapter<RecyclerView.ViewHolder>() {

private val groups: ArrayList<Group> = ArrayList()

private var recyclerViewPool = RecyclerView.RecycledViewPool()

[...]

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
    return when (viewType) {
        CATEGORIES_LIST.typeText.hashCode() -> {
            val holder = CategoryGroupViewHolder(
                DataBindingUtil.inflate(
                    LayoutInflater.from(parent.context),
                    R.layout.group_item_categories_list, parent, false
                ), adapterCallback
            )
            holder.binding.recyclerView.setRecycledViewPool(recyclerViewPool)
            holder
        }
     
        [...]

So I'm basically setting the viewPool to the nested RVs in onCreateViewHolder. On the top of that, following this article: https://medium.com/@thagikura/reduce-the-number-of-inflation-of-viewholders-drastically-by-sharing-a-viewpool-across-multiple-249d5fc6d28 I have also done the following thing in the viewholder:

class CategoryGroupViewHolder(
   val binding: GroupItemCategoriesListBinding,
   private val adapterCallback: adapterCallback?
):
RecyclerView.ViewHolder(binding.root) {

private val categoryAdapter = CategoryAdapter()
private val defaultItemAnimator = DefaultItemAnimator()
private val linearLayoutManager = LinearLayoutManager(
    binding.root.context, LinearLayoutManager.HORIZONTAL, false
)

fun bind(group: Group) = with(binding.root) {
    binding.categoryGroup = group
    binding.executePendingBindings()
    linearLayoutManager.initialPrefetchItemCount = 5
    binding.recyclerView.apply {
        adapter = categoryAdapter
        linearLayoutManager.recycleChildrenOnDetach = true
        layoutManager = linearLayoutManager
        itemAnimator = defaultItemAnimator
    }
}

Notice linearLayoutManager.recycleChildrenOnDetach = true. What am I doing wrong here and why are my items completely mixing up in the entire adapter. Any advice on how to properly use this recycledViewPool?

Also, if any of you have some advice on how to optimize the vertical recyclerView in vertical recyclerView, that would be very much appreciated. Thanks

Answer 1

If I'm not mistaken, I think using ConcatAdapter here will solve your problem in a much simpler way. If you look for an example, you can look at my repo.

https://github.com/cnrture/ConcatAdapterExample