Single Activity login flow Android

Question

I am currently working on a school project that displays your timetable, grades, subjects and so on. To use any functionality in the Android application you have to be logged in. Here comes my problem:

When the users starts the application for the first time, they should see a login fragment. Once the login is completed they will be presented with a setup screen where they can choose color themes for grades and other user specific things. Only then should they be presented with the actual main fragment. On the second start the user should directly see the main fragment

The main fragment is a FragmentContainerView and a BottomNavigationBar that hosts 5 other fragments. In each of those subfragments you can click on items. Then a different fragment should be presented that shows some more details. These fragments however should overlap the bottom navigation so that you have to navigate back before you can choose a different fragment in the bottom navigation bar.

As far as I can tell I need nested FragmentContainerViews. The MainActivity should be

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host_fragment_activity_main"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

The MainActivity should host the LoginFragment, SetupFragment and a MainFragment. In the MainFragment should be like this

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav_view"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/bottom_nav_menu" />

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host_fragment_activity_main"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constrainedHeight="true"
        app:layout_constraintBottom_toTopOf="@+id/nav_view"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/mobile_navigation" />

</androidx.constraintlayout.widget.ConstraintLayout>

I would like to achieve all of this with a navigation graph. Do I have to use one graph or two for each FragmentContainerView? Then there is also the problem with the detail Fragments. If for example I have a HomeFragment as a child of the MainFragment which is a child of the MainActivity and in the HomeFragment the user clicks on for example a button to the SettingsFragment, this fragment should be displayed as a child of the MainActivity. How would I get this working? I've already had a look at this question but don't really understand how to implement it. How to setup Multiple nested FragmentContainerViews with respective navigation graphs?

Could somebody maybe create a very simple implementation of this. I especially need help with the nested FragmentContainerViews, the BottomNavigationBar and the NavigationGraph. I've also come across the problem that the bottom navigation bar doesn't respond anymore. Thanks for your help in advance. Please let me know if you need any more details.

Answer 1

1.way

val homeFragment = HomeFragment()
val listFragment = ListFragment()
val profileFragment = ProfileFragment()

nav_view.setOnItemSelectedListener {
                when (it) {
                    R.id.homeFragment -> setCurrentFragment(homeFragment)
                    R.id.listFragment -> setCurrentFragment(listFragment)
                    R.id.profileFragment -> 
                    setCurrentFragment(profileFragment)
                }
                return@setOnItemSelectedListener
            }



private fun setCurrentFragment(fragment: Fragment) =
        supportFragmentManager.beginTransaction().apply {
            replace(R.id.nav_host_fragment_activity_main, fragment)
            addToBackStack(null) //If you delete this, press the back button, it will not return to the previous fragment.
            commit()
        }

2.way

Navigation with

https://www.youtube.com/watch?v=DI0NIk-7cz8&t=527s&ab_channel=Stevdza-San