Layout behavior for Bottom Navigation View to hide and show on scroll. Root ViewGroup should be CoordinatorLayout.

BottomNavigationViewBehavior.kt

class BottomNavigationViewBehaviour(context: Context, attrs: AttributeSet) : CoordinatorLayout.Behavior<BottomNavigationView>(context, attrs) {

    private var height: Int = 0

    override fun onLayoutChild(parent: CoordinatorLayout?, child: BottomNavigationView?, layoutDirection: Int): Boolean {
        height = child!!.height
        return super.onLayoutChild(parent, child, layoutDirection)
    }

    override fun onStartNestedScroll(coordinatorLayout: CoordinatorLayout, child: BottomNavigationView, directTargetChild: View, target: View, axes: Int, type: Int): Boolean {
        return axes == ViewCompat.SCROLL_AXIS_VERTICAL
    }

    override fun onNestedScroll(coordinatorLayout: CoordinatorLayout, child: BottomNavigationView, target: View, dxConsumed: Int, dyConsumed: Int, dxUnconsumed: Int, dyUnconsumed: Int, type: Int) {
        if (dyConsumed > 0) {
            child.visibility = View.INVISIBLE
            slideDown(child)
        } else if (dyConsumed < 0) {
            child.visibility = View.VISIBLE
            slideUp(child)
        }
    }

    private fun slideUp(child: BottomNavigationView) {
        child.clearAnimation()
        child.animate().translationY(0f).duration = 200
    }

    private fun slideDown(child: BottomNavigationView) {
        child.clearAnimation()
        child.animate().translationY(height.toFloat()).duration = 200
    }
}