Handle onBackPressed in Android Navigation Component

Question

I have implemented navigation Drawer with Navigation Components in Android. I have 5 fragments that I want to go back to my HomeFragment when I click on back pressed. For the moment they stay onBackStack and do not go to my desired fragment but go to whatever fragment was first. This is my nav_graph :

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
            xmlns:app="http://schemas.android.com/apk/res-auto"
            xmlns:tools="http://schemas.android.com/tools"
            app:startDestination="@id/setupFragment"
            android:id="@+id/treasure_nav"
            android:label="Pick a country">
    <fragment android:id="@+id/homeFragment"
              android:name="com.stavro_xhardha.pockettreasure.ui.home.HomeFragment"
              android:label="Home"
              tools:layout="@layout/fragment_home">
        <action android:id="@+id/action_home_fragment_to_namesFragment2"
                app:popUpTo="@id/homeFragment"
                app:destination="@id/namesFragment"/>
        <action android:id="@+id/action_home_fragment_to_quranFragment"
                app:popUpTo="@id/homeFragment"
                app:destination="@id/quranFragment"/>
        <action android:id="@+id/action_homeFragment_to_tasbeehFragment"
                app:popUpTo="@id/homeFragment"
                app:destination="@id/tasbeehFragment"/>
        <action android:id="@+id/action_homeFragment_to_galleryFragment"
                app:popUpTo="@id/homeFragment"
                app:destination="@id/galleryFragment"/>
        <action android:id="@+id/action_homeFragment_to_newsFragment"
                app:popUpTo="@id/homeFragment"
                app:destination="@id/newsFragment"/>
        <action android:id="@+id/action_homeFragment_to_settingsFragment"
                app:popUpTo="@id/homeFragment"
                app:destination="@id/settingsFragment"/>
    </fragment>
    <fragment
            android:id="@+id/namesFragment"
            android:name="com.stavro_xhardha.pockettreasure.ui.names.NamesFragment"
            android:label="Names of Allah"
            tools:layout="@layout/fragment_names"/>
    <fragment
            android:id="@+id/quranFragment"
            android:name="com.stavro_xhardha.pockettreasure.ui.quran.QuranFragment"
            android:label="Quran"
            tools:layout="@layout/fragment_quran"/>
    <fragment android:id="@+id/tasbeehFragment"
              android:name="com.stavro_xhardha.pockettreasure.ui.tasbeeh.TasbeehFragment"
              android:label="Tasbeeh"
              tools:layout="@layout/fragment_tasbeeh"/>
    <fragment android:id="@+id/galleryFragment"
              android:name="com.stavro_xhardha.pockettreasure.ui.gallery.GalleryFragment"
              android:label="Gallery"
              tools:layout="@layout/fragment_gallery"/>
    <fragment android:id="@+id/newsFragment"
              android:name="com.stavro_xhardha.pockettreasure.ui.news.NewsFragment"
              android:label="News"
              tools:layout="@layout/fragment_news"/>
    <fragment android:id="@+id/settingsFragment"
              android:name="com.stavro_xhardha.pockettreasure.ui.settings.SettingsFragment"
              android:label="Settings"
              tools:layout="@layout/fragment_settings"/>
    <fragment android:id="@+id/setupFragment"
              android:name="com.stavro_xhardha.pockettreasure.ui.setup.SetupFragment"
              android:label="Pick country"
              tools:layout="@layout/fragment_setup">
        <action android:id="@+id/action_setupFragment_to_homeFragment3"
                app:destination="@+id/homeFragment"
                app:launchSingleTop="true"
                app:popUpTo="@+id/treasure_nav"
                app:popUpToInclusive="true"/>
    </fragment>
</navigation>

And this is my onBackPressed in my MainActivity (and the only one) :

override fun onBackPressed() {
        if (drawer_layout.isDrawerOpen(GravityCompat.START)) {
            drawer_layout.closeDrawer(GravityCompat.START)
        } else {
                super.onBackPressed()
        }
    }

Edit: When i remove the super.onBackPressed() and replace it with : findNavController(R.id.nav_host_fragment).popBackStack(R.id.homeFragment, false) I achieve what I want. The only problem is that when I am in the homeFragment I want to end the app but I can't.

Answer 1

I made this extension function to do just that:

fun Fragment.setupOnBackPressedCallback(block: () -> Unit) {
    requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner,
        object : OnBackPressedCallback(true) {
            override fun handleOnBackPressed() = block.invoke()
        }
    )
}

Inside your fragment, all you have to do is call it passing a lambda:

setupOnBackPressedCallback {
    // Do what you want when you press the back button
}

Answer 2

If my understanding is correct, you want to go back to HomeFragment wherever you are in the navigation flow. For this case you could try registering OnBackPressedCallback on your Fragments via addOnBackPressedCallback, and call popBackStack to navigate to your HomeFragment. Try adding this to Fragments' onViewCreated that need to go back to HomeFragment on backpress:

@Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        navController = Navigation.findNavController(view);

        requireActivity().addOnBackPressedCallback(getViewLifecycleOwner(), () -> {
               navController.popBackStack(R.id.homeFragment, false);
            });
            return true;
        });

Answer 3

If you want to close app when press back in HomeFragment, it's just specified these attributes of the last action that navigates you to this destination:

1. app:popUpToInclusive to true
2. app:popUpTo to of the last fragment(SetupFragment) that navigates you here(HomeFragment)

It means change your code like this:

<fragment android:id="@+id/setupFragment"
          android:name="com.stavro_xhardha.pockettreasure.ui.setup.SetupFragment"
          android:label="Pick country"
          tools:layout="@layout/fragment_setup">
    <action android:id="@+id/action_setupFragment_to_homeFragment3"
            app:destination="@+id/homeFragment"
            app:launchSingleTop="true"
            app:popUpTo="@+id/setupFragment"          // this line changes
            app:popUpToInclusive="true" />            // and this requires too
</fragment>