Android navigation architecture component - system's back button exits the app

Question

I am making a demo using android's navigation architecture component. I have an activity and two fragments.

In the activity's xml, I have added the following code-

<fragment
    android:id="@+id/main_container"
    android:name="androidx.navigation.fragment.NavHostFragment"
    android:layout_width="@dimen/match_constraints"
    android:layout_height="@dimen/match_constraints"
    app:defaultNavHost="true"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:navGraph="@navigation/nav_graph" />

And then I have set the first fragment as the start destination. In the first fragment, on a button's click I have done following -

NavHostFragment.findNavController(this).navigate(R.id.action_firstFragment_to_secondFragment)

And it works fine. Now when I press system's back button, ideally I should go back to first fragment, but the app exits. What am I doing wrong?

Answer 1

I suppose, this is occurring in your code just because you might be handling the onBackPressed() functionality somewhere in your BaseActivity. Please look carefully.

I hope, this helps you.