AnimationViewUtils.kt

fun View.expandOrCollapse(expand: Boolean) {
    if (expand) expand() else collapse()
}

fun View.expand() {
    val matchParentMeasureSpec = View.MeasureSpec.makeMeasureSpec((parent as View).width, View.MeasureSpec.EXACTLY)
    val wrapContentMeasureSpec = View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED)
    measure(matchParentMeasureSpec, wrapContentMeasureSpec)

    val targetHeight = measuredHeight
    var actualHeight = layoutParams.height

    if (actualHeight <= 0) {
        actualHeight = 1
        layoutParams.height = 1
    }

    visibility = View.VISIBLE

    val anim = object : Animation() {
        override fun applyTransformation(interpolatedTime: Float, t: android.view.animation.Transformation?) {
            layoutParams.height =
                if (interpolatedTime == 1f) ViewGroup.LayoutParams.WRAP_CONTENT
                else actualHeight + ((targetHeight - actualHeight) * interpolatedTime).toInt()
            requestLayout()
        }

        override fun willChangeBounds() = true
    }

    // Expansion speed of 1dp/ms
    anim.duration = (targetHeight / context.resources.displayMetrics.density).toInt().toLong()
    startAnimation(anim)
}

fun View.collapse() {
    val initialHeight = measuredHeight

    val anim = object : Animation() {
        override fun applyTransformation(interpolatedTime: Float, t: android.view.animation.Transformation?) {
            if (interpolatedTime == 1f)
                visibility = View.GONE
            else {
                layoutParams.height = initialHeight - (initialHeight * interpolatedTime).toInt()
                requestLayout()
            }
        }

        override fun willChangeBounds() = true
    }

    // Collapse speed of 1dp/ms
    anim.duration = (initialHeight / context.resources.displayMetrics.density).toInt().toLong()
    startAnimation(anim)
}