LauncherActivity.kt

companion object {
        /** The magnitude of rotation while the list is scrolled. */
        private const val SCROLL_ROTATION_MAGNITUDE = 0.25f

        /** The magnitude of rotation while the list is over-scrolled. */
        private const val OVERSCROLL_ROTATION_MAGNITUDE = -10

        /** The magnitude of translation distance while the list is over-scrolled. */
        private const val OVERSCROLL_TRANSLATION_MAGNITUDE = 0.2f

        /** The magnitude of translation distance when the list reaches the edge on fling. */
        private const val FLING_TRANSLATION_MAGNITUDE = 0.5f
}


rvApps.edgeEffectFactory = object : RecyclerView.EdgeEffectFactory() {
            override fun createEdgeEffect(recyclerView: RecyclerView, direction: Int): EdgeEffect {
                return object : EdgeEffect(recyclerView.context) {

                    override fun onPull(deltaDistance: Float) {
                        super.onPull(deltaDistance)
                        handlePull(deltaDistance)
                    }

                    override fun onPull(deltaDistance: Float, displacement: Float) {
                        super.onPull(deltaDistance, displacement)
                        handlePull(deltaDistance)
                    }

                    private fun handlePull(deltaDistance: Float) {
                        // This is called on every touch event while the list is scrolled with a finger.
                        // We simply update the view properties without animation.
                        val sign = if (direction == DIRECTION_BOTTOM) -1 else 1
                        val rotationDelta = sign * deltaDistance * OVERSCROLL_ROTATION_MAGNITUDE
                        val translationYDelta =
                            sign * recyclerView.width * deltaDistance * OVERSCROLL_TRANSLATION_MAGNITUDE
                        recyclerView.forEachVisibleHolder { holder: AppViewHolder ->
                            holder.rotation.cancel()
                            holder.translationY.cancel()
                            holder.itemView.rotation += rotationDelta
                            holder.itemView.translationY += translationYDelta
                        }
                    }

                    override fun onRelease() {
                        super.onRelease()
                        // The finger is lifted. This is when we should start the animations to bring
                        // the view property values back to their resting states.
                        recyclerView.forEachVisibleHolder { holder: AppViewHolder ->
                            holder.rotation.start()
                            holder.translationY.start()
                        }
                    }

                    override fun onAbsorb(velocity: Int) {
                        super.onAbsorb(velocity)
                        val sign = if (direction == DIRECTION_BOTTOM) -1 else 1
                        // The list has reached the edge on fling.
                        val translationVelocity = sign * velocity * FLING_TRANSLATION_MAGNITUDE
                        recyclerView.forEachVisibleHolder { holder: AppViewHolder ->
                            holder.translationY
                                .setStartVelocity(translationVelocity)
                                .start()
                        }
                    }
                }
            }
        }