BottomNavigationFABBehavior.kt

class BottomNavigationFABBehavior(context: Context?, attrs: AttributeSet?) : CoordinatorLayout.Behavior<View>(context, attrs) {

    override fun layoutDependsOn(parent: CoordinatorLayout, child: View, dependency: View): Boolean {
        return dependency is Snackbar.SnackbarLayout
    }

    override fun onDependentViewRemoved(parent: CoordinatorLayout, child: View, dependency: View) {
        child.translationY = 0f
    }

    override fun onDependentViewChanged(parent: CoordinatorLayout, child: View, dependency: View): Boolean {
        return updateButton(child, dependency)
    }

    private fun updateButton(child: View, dependency: View): Boolean {
        if (dependency is Snackbar.SnackbarLayout) {
            val oldTranslation = child.translationY
            val height = dependency.height.toFloat()
            val newTranslation = dependency.translationY - height
            child.translationY = newTranslation

            return oldTranslation != newTranslation
        }
        return false
    }
}