How can I back from the second fragment to the first fragment using Navigation Component?

navigation_main.xml

<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"
    android:id="@ id/main_navigation"
    app:startDestination="@id/firstFragment">

    <fragment
        android:id="@ id/firstFragment"
        android:name="com.test.ttt.FirstFragment"
        tools:layout="@layout/fragment_first">

        <action
            android:id="@ id/action_firstFragment_to_secondFragment"
            app:destination="@id/secondFragment"
            app:popUpTo="@id/firstFragment" 
            app:popUpToInclusive="true"/>

    </fragment>

    <fragment
        android:id="@ id/secondFragment"
        android:name="com.test.ttt.SecondFragment"
        tools:layout="@layout/fragment_second" />

</navigation>

FirstFragment.java

public class FirstFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        Navigation.findNavController(container).navigate(FirstFragmentDirections.actionFirstFragmentToSecondFragment());
        return inflater.inflate(R.layout.fragment_first, container, false);
    }

}

I want when I press the back button in the second fragment, It must back to the first fragment but currently, When I press the back button in the second fragment it is leaving the app.

How can I solve this problem?

CodePudding user response：

The reason you are being exited from the app is because while navigating to the second fragment, you are removing the first fragment from your stack. The properties app:popUpTo and app:popUpToInclusive are typically used when you want to remove some fragments from your backstack while navigating. A simple use case for this would be when navigating from Login/SignUp Fragment to Home/Main Fragment. In this case you would not want the user to be able to press back and go back to login/signup screens. Here is where the two properties would help.

TL;DR - Remove the app:popUpTo and app:popUpToInclusive properties from your action

Change

    <action
        android:id="@ id/action_firstFragment_to_secondFragment"
        app:destination="@id/secondFragment"
        app:popUpTo="@id/firstFragment" 
        app:popUpToInclusive="true"/>

to

    <action
        android:id="@ id/action_firstFragment_to_secondFragment"
        app:destination="@id/secondFragment"/>