For Medium article "Animate Everything! (Android Animation Showcase)"

ItemsInOutAnimation.kt

fun animateItemsOut() = animate(R.anim.item_animation_out)

fun animateItemsIn() = animate(R.anim.item_animation_in)

private fun animate(@AnimRes animationId: Int) {
    var startOffset = 0L
    for (i in childCount - 1 downTo 0) {
        val set = AnimationUtils.loadAnimation(context, animationId)
        set.startOffset = startOffset
        getChildAt(i)?.startAnimation(set)
        startOffset += ANIMATION_OFFSET
        set.withEndActionOnce { updateViews() }
    }
}