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Today I've started playing with Android's Navigation Component to implement authentication flow in my app. The idea is very simple: a user launches the app and it displays one piece of UI if she's authenticated and another if she's not.

What I've done is in my HomeFragment's onViewCreated method I check if a user is authenticated and if she's not I call the NavController's navigate() method by passing it the id of an action that will navigate to the AuthenticationFragment. Everything works fine until a user clicks the back button while in AuthenticationFragment, because then I get this error. I still have no idea what's the actual reason for that error, but the idea of navigation happening too quickly seems similar to my case: the destinations first switch from AuthenticationFragment to HomeFragment and then immediately from HomeFragment to AuthenticationFragment again, because HomeFragment finds out again that a user is not authenticated.

Despite of the error I'm getting, this approach still seems wrong to me. The user shouldn't be able to go back to the HomeFragment (and see the screen flicker when fragments are immediately switching back and forth) before she authenticates. I've also looked at this Android's official guide to implementing an authentication flow, but it too seems wrong to me, because a redundant third piece of UI is involved there (the MainFragment). I could replace it with a splash screen in my case, but it would still stay in the back stack and the user would be able to go back to splash screen, which is obviously nonsense.

So what would be the correct way to implement an authentication flow using the Android's new Navigation Component? The functionality I want is: if a user is not authenticated, then she's redirected to an authentication UI and if she presses the back button from there she should exit the application.

UPDATE: I know I could just listen to the back press event and close the application from there, but I still hope there's some elegant solution using Android's Navigation Component.

Salivan
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    Try to add to action that navigating to login fragment - app:popUpTo="@id/homeFragment" and app:popUpToInclusive="true" – Alex Mar 18 '19 at 12:55

1 Answers1

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In your login fragment, you need to declare "Pop up-to" action from home fragment.

  1. This pops all non-matching destinations from the back stack until this destination is found.

  2. "popUpToInclusive = true" pops the given destination from backstack

    <fragment android:id="@+id/loginFragment" android:name="com.example.navigationsample.fragments.Login" android:label="Login_Fragment" tools:layout="@layout/layout_login"> <action android:id="@+id/action_loginFragment_to_homeFragment" app:destination="@id/homeFragment" app:popUpTo="@id/loginFragment" app:popUpToInclusive="true"/> </fragment>

Varsha Ravikumar
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