RecycleView's setInitialPrefetchItemCount is not working

Question

I'm trying to improve the user experience while scrolling a grid of images by prefetching views ahead of time using the new API introduced in the support library 25.1 for controlling the number of prefetched items in a RecycleView.

GridLayoutManager layoutManager = new GridLayoutManager(this.getContext(), PhotoGridViewHolder.SPAN_SIZE);
layoutManager.setItemPrefetchEnabled(true);
layoutManager.setInitialPrefetchItemCount(30); 
photosRecycleView.setLayoutManager(layoutManager);
... add 100 photos to the adapter ...

And I also added logging for my ViewHolders so I could see if the binding really happened.

void bind(final Photo photo, int position) {
    // I expcet to see 30 logs without event scrolling as the intial set to 30.
    log.d("binding photo: " + photo.getId());
    loadPhoto(photo);
}

However, it seems like it's not working, as I loaded a list of 100 images but I see only a few log entries (just fetching the visible items), but I'd expect to see at 30 as I set it to be like so.

Answer 1

As @FlanschiFox and comments below his answer says, this is only working for inner RecyclerViews. Additionally, I wrote a PreloadLinearLayoutManager here to preload data 5 items before the list scrolls to the end. It may help you a bit.

Answer 2

According to the docs, this is only working for inner RecyclerViews.

Documentation: isItemPrefetchEnabled

Sets the number of items to prefetch in collectInitialPrefetchPositions(int, LayoutPrefetchRegistry), which defines how many inner items should be prefetched when this LayoutManager's RecyclerView is nested inside another RecyclerView.