How do I know how many items the RecyclerView is going to inflate?

Question

I have a RecyclerView.Adapter together with a list of items. At some point I will make some changes to this list and then I will call notifyDataSetChanged() (or another similar method). How do I know how many ViewHolders will be created prior to making this call? Or how many times onBindViewHolder will be called? Ideally I should know one of these numbers before calling this notify method, but I could also manage with receiving a callback when the adapter finishes to make all the work (inflations, bindings). From my experiments, the adapter is not done with the work right after calling notifyDataSetChanged.

I need to know how many items will be or were inflated. Ideally 'will be'. Some ideas on how I can achieve this?

UPDATE

Stumbled upon: Is there a callback for when RecyclerView has finished showing its items after I've set it with an adapter?, which gave me an answer to the second thing I asked: "I could also manage with receiving a callback when the adapter finishes to make all the work (inflations, bindings)."

I made some modifications to the accepted answer and the following Log only displays after all the recycler's items were inflated (at least in my app):

RecyclerView(context).apply {
layoutManager = object: LinearLayoutManager(context, VERTICAL, false) {
    override fun onLayoutCompleted(state: RecyclerView.State?) {
        super.onLayoutCompleted(state)
        val firstVisibleItemPosition = findFirstVisibleItemPosition()
        val lastVisibleItemPosition = findLastVisibleItemPosition()
        if(firstVisibleItemPosition == -1 || lastVisibleItemPosition == -1)
            return
        Log.d("RECYCLER", "all sync inflations done")
    }
}

}

Answer 1

How do I know how many ViewHolders will be created prior to making this call? Or how many times onBindViewHolder will be called?

Sorry, there is no way to know that. It will depend on all sorts of variables which are not known until rendering is being done.

For example, suppose that your RecyclerView is a vertically-scrolling list of rows, and each row shows some text in a TextView. How many rows will be needed will depend on:

• What the text is, which could be short or long
• What the row layout is and how it calls for that text to be rendered (font, font scale, padding, margin, etc.)
• What the font scale is
• What the RecyclerView size is (which in turn varies based on things like window size, which in turn varies based on things like screen size and whether we are in split-screen or multi-window mode, etc.)

And, in terms of how many ViewHolder objects will be instantiated, that will also depend on whether this is the first time the RecyclerView has been shown or whether you are updating an existing one with new data.

And that is just for very simple rows. More complex rows would add more dependencies.

Ideally I should know one of these numbers before calling this notify method

That is unrealistic. My guess it that is unnecessary. You might consider asking a separate Stack Overflow question where you explain why you feel that you need this, and perhaps we can suggest alternative approaches to solving your perceived problem. IOW, your question feels like an XY problem, where you have guessed at a solution to some other problem.