fastSmoothScrollToPosition(int position) extension for RecycleView
Suppose you have a list with many items. The app wants to select a certain item and also scroll to it to show it to you.
RecyclerView is the standard tool for showing collections of data on the screen in Android, and nofifyItemChanged is one of the optimisations that make it performance efficient and visually appealing.
The item change would look like this:
// tell the adapter that the item changed, and it (but nothing else) needs to be redrawn if it is on screen
recyclerView.adapter.notifyItemChanged(position)
Let's see how well it works with scrolling... we have 2 options:
As the name shows, a smooth scrolling animation is nice to look at and keeps us in the context. We visually see how we got to that item.
But what if the list is long? It will scroll at a constant pace, through all the items in between, with a full render of each. This can get into a long and annoyng wait:
This behaviour was described in the StylingAndroid Blog since 2015.
Unhappy with the long wait, we could give up the whole idea of animation. Just snap us to the item, a frame change should we quick, right?
But no, it looks like any scrollToPosition() made after notifyItemChanged() results in some nasty animated curtain wipe effect or I don't know how to call it:
This is a RecyclerView Bug logged in March 2019.
This new function offers a reasonable UX alternative to scrollToPosition and smoothScrollToPosition. It has some smoothness, and it doesn't take forever. The logic is:
- if we are far away from the desired position, jump closer, within a few screens' coverage
- then do a smooth scroll until we reach the position
Just click the badge for instructions:
Just call the function directly on your RecyclerView. That's it.
recyclerView.fastSmoothScrollToPosition(newPosition)
This extension supports any RecyclerView backed by a LinearLayoutManager or GridLayoutManager:
You can change the number of screens we consider in proximity. It is a float. Default is 3.0. Less than 3 screens distance may be not enough to wear off the nasty side-effect seen with scrollToPosition. More screens are fine, but then the wait gets longer.
FastSmoothScroll.bufferScreens = 4.5
You can enable logging and change the Log TAG if you want. Should not make any difference in performance.
FastSmoothScroll.logging = true
FastSmoothScroll.logTag = "FSS"