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.

Univocal

couldnt understand the problem from your statment. can you elaborate what actually you want to do on backPress? I have concluded two situations from your statement. One if you have selected any item from nav, then on backpress you want to go to home screen. and again on backpress want to exit the app. Second that on back press you want to change the fragment to home and exit immediate. – Pyroxylin

first of all when you are replacing fragments over eachother, you have to use replace fragment instead of add fragment so that they wont stay in backStack – Pyroxylin

where do you see the replace or the add method o.O – Univocal

Answer 1

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;
        });

Hinch

You did solve my issue although looks like I'm having a lower API, and I am going to update the answer a little – Univocal

Answer 2

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>

Annelieseannelise

No, I am already ok with that. What I need is that when I go from HomeFragment to fragment Gallery, and than to fragment Settings, and than press back, it sends me to the Settings fragment. I dont want this , I want to get back to HomeFragment – Univocal

You are in settings and after press back it sends you to settings? wow! – Annelieseannelise

hello, im really sory about that. it was a mistake: To make the case clear: When Navigate from Home -> GalleryFragment -> SettingsFragment. On SettingsFragment when I press back, it sends me to the GalleryFragment. I want to go to HomeFragment. – Univocal

this doesn't work also :( – Heliochrome

Answer 3

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
}

Mallemuck