SnapHelper tip: Limit the time a scroll takes

snaphelpertip2.kt

private const val MILLISECONDS_PER_INCH = 100
private const val MAX_SCROLL_ON_FLING_DURATION = 250 // ms

override fun createSnapScroller(layoutManager: LayoutManager?): LinearSmoothScroller? {
    if (layoutManager !is ScrollVectorProvider) return null
    return object : LinearSmoothScroller(context) {
        override fun onTargetFound(targetView: View?, state: State?, action: Action?) {
            if (targetView == null) return
            val snapDistances = calculateDistanceToFinalSnap(layoutManager, targetView)
            val dx = snapDistances[0]
            val dy = snapDistances[1]
            val time = calculateTimeForDeceleration(Math.max(Math.abs(dx), Math.abs(dy)))
            if (time > 0) {
                action?.update(dx, dy, time, mDecelerateInterpolator)
            }
        }

        override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics?): Float =
                MILLISECONDS_PER_INCH / displayMetrics.densityDpi

        override fun calculateTimeForScrolling(dx: Int): Int =
                Math.min(MAX_SCROLL_ON_FLING_DURATION, super.calculateTimeForScrolling(dx))
    }
}