Solution for controlling the speed of the scroll, to scroll faster to more distant positions
A bit late to the party, but here's a Kotlin solution for anyone else looking.
This proves tricky to solve by overriding calculateSpeedPerPixel of the LinearSmoothScroller. With that attempt for a solution I was getting a lot of "RecyclerView passed over target position" errors. If anyone has an idea how to solve those please share.
I took a different approach with this solution: first jump to a position closer to the target position and then smooth scroll:
/**
* Enables still giving an impression of difference in scroll depending on how far the item scrolled to is,
* while not having that tedious huge linear scroll time for distant items.
*
* If scrolling to a position more than minJumpPosition diff away from current position, then jump closer first and then smooth scroll.
* The distance how far from the target position to jump to is determined by a logarithmic function,
* which in our case is y=20 at x=20 and for all practical purposes never goes over a y=100 (@x~1000) (so max distance is 100).
*
* If the diff is under 20 there is no jump - for diff 15 the scroll distance is 15 items.
* If the diff (x) is 30, jumpDiff (y) is around 28, so jump 2 and scroll 28 items.
* If the diff (x) is 65, jumpDiff (y) is around 44, so jump 21 and scroll 44 items.
* If the diff (x) is 100, jumpDiff (y) is around 53, so jump 47 and scroll 53 items.
* If the diff (x) is 380, jumpDiff (y) is around 80, so jump 300 and scroll 80 items.
* If the diff (x) is 1000, jumpDiff (y) is around 100 items scroll distance.
* If the diff (x) is 5000, jumpDiff (y) is around 133 items scroll distance.
* If the diff (x) is 8000, jumpDiff (y) is around 143 items scroll distance.
* If the diff (x) is 10000, jumpDiff (y) is around 147 items scroll distance.
*
* You can play with the parameters to change the:
* - minJumpPosition: change when to start applying the jump
* - maxScrollAllowed: change speed change rate (steepness of the curve)
* - maxPracticalPosition: change what is the highest expected number of items
* You might find it easier with a visual tool:
* https://www.desmos.com/calculator/auubsajefh
*/
fun RecyclerView.jumpThenSmoothScroll(smoothScroller: SmoothScroller, position: Int,
delay: Long = 0L,
doAfterScrolled: (() -> Unit)? = null) {
smoothScroller.targetPosition = position
val layoutManager = layoutManager as LinearLayoutManager
fun smoothScrollAndDoAfter() {
layoutManager.startSmoothScroll(smoothScroller)
doAfterScrolled?.let { post { postDelayed({ doAfterScrolled() }, max(0L, delay)) } }
}
val firstVisiblePosition = layoutManager.findFirstVisibleItemPosition()
val diff = abs(position - firstVisiblePosition).toFloat()
// Position from which to start applying "jump then scroll".
val minJumpPosition = 20f
if (diff > minJumpPosition) {
// On the logarithmic function graph,
// y=minJumpPosition when x=minJumpPosition, and y=maxScrollAllowed when x=maxPracticalPosition.
// So we are using two points to determine the function:
// (minJumpPosition, minJumpPosition) and (maxPracticalPosition, maxScrollAllowed)
// In our case (20, 20) and (1000, 100)
// Max practical possible items (max diff between current and target position).
// It is OK for this to be high as logarithmic function is long approaching this value.
val maxPracticalPosition = 1000
// Never scroll more than this number of items.
// Scroll will be from 0 to maxScrollAllowed for all practical purposes
// ("practical" as determined by maxPracticalPosition).
val maxScrollAllowed = 100
// b = (x2/x1)^(1f/(y2-y1))
val logBase = (maxPracticalPosition / minJumpPosition).pow (1f / (maxScrollAllowed - minJumpPosition))
// s = (log(b)x1) - y1
val logShift = log(minJumpPosition, logBase) - minJumpPosition
val jumpDiff = (log(diff, logBase) - logShift).toInt() // y: 20 to 100 (for diff x: 20 to 1000)
val jumpDiffDirection = if (position < firstVisiblePosition) 1 else -1
val jumpPosition = position + (jumpDiff * jumpDiffDirection)
// First jump closer
layoutManager.scrollToPositionWithOffset(jumpPosition, 0)
// Then smooth scroll
smoothScrollAndDoAfter()
} else {
smoothScrollAndDoAfter()
}
}
