how to hide BottomNavigationView on android-navigation lib

You could do something like this in your activity’s onCreate. When ever an item in the nav bar is selected it will show or hide the nav based on the fragment id’s.

private fun setupNav() {
    val navController = findNavController(R.id.nav_host_fragment)
    findViewById<BottomNavigationView>(R.id.bottomNav)
        .setupWithNavController(navController)

    navController.addOnDestinationChangedListener { _, destination, _ ->
        when (destination.id) {
            R.id.mainFragment -> showBottomNav()
            R.id.mineFragment -> showBottomNav()
            else -> hideBottomNav()
        }
    }
}

private fun showBottomNav() {
    bottomNav.visibility = View.VISIBLE
    
}

private fun hideBottomNav() {
    bottomNav.visibility = View.GONE
   
}