Optimizing Nested RecyclerView

A RecyclerView is more advanced version of ListView which reuses the same view to prevent additional creation of views to provide a smooth scrolling experience. The RecyclerView achieves this by keeping a View pool that holds the views that are no longer visible and can be recycled.

Sometimes we need to nest RecyclerViews to create some layouts. Consider the case where you have a horizontal RecyclerView inside a Vertical RecyclerView.

In the Image you can see vertical scroling list of horizontal scroling lists.This is achieved by placing a recyclerView inside another recyclerView.

When the user swipes the side-wise the inner RecyclerView recycles the views and gives you a smooth scroll. But this is not the case when the user scrolls vertically. Each of the views of the inner RecyclerView is inflated again. This is because each of the the nested RecyclerViews has a view pool of its own.

We can fix this by setting a single view pool for all the inner RecyclerViews.

RecyclerView.setRecycledViewPool(RecycledViewPool) allows you to set a custom view pool to your recyclerView. The code looks like this

public OuterRecyclerViewAdapter(List<Item> items) {
    //Constructor stuff
    viewPool = new RecyclerView.RecycledViewPool();
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    //Create viewHolder etc
    holder.innerRecyclerView.setRecycledViewPool(viewPool);
    
}

So now as all the inner RecyclerViews have the same view pool, it can use each other’s scraped views. Which gives much lesser view creation and better scroll performance.