NavigationDelegate.kt

class NavigationDelegate(private val fragmentManager: FragmentManager,
                         private val containerId: Int) {
    
    init {
        fragmentManager.addOnBackStackChangedListener {
            val currentFragment = fragmentManager.findFragmentById(containerId)
            currentFragment.userVisibleHint = true
        }
    }

    public fun navigate(from: Fragment? = null, to: Fragment, addToBackStack: Boolean = true) {
        if(from != null) from.userVisibleHint = false

        val transaction = fragmentManager.beginTransaction()
                .add(containerId, to)
        if(addToBackStack) transaction.addToBackStack(null)
        transaction.commit()
    }
}