how to implement Conditional Navigation in navigation architecture components

Question

In the new Navigation architecture component, how to implement conditional navigation?

Currently I have a single activity with LoginFragment and HomeFragment. Based on a certain login_flag, I used to call either fragment from the MainActivity. Since LoginFragment is called only once, I have set the startDestination to HomeFragment and the Navigation loads this HomeFragment. is there any way to check the login_flag before the Navigation loads the HomeFragment.

Answer 1

This is how I deal with conditional navigation :

1. Set HomeFragment as the start destination

2. Create a global action for LoginFragment

   <action
       android:id="@+id/action_global_loginFragment"
       app:destination="@id/loginFragment"
       app:launchSingleTop="false"
       app:popUpTo="@+id/nav_graph"
       app:popUpToInclusive="true" />
   

3. Perform conditional navigation inside onViewCreated :

   // HomeFragment.kt
   override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
       super.onViewCreated(view, savedInstanceState)
   
       if(!appAuth.isAuthenticated()) {
           view.findNavController().navigate(R.id.action_global_loginFragment)
       }
   }
   

Answer 2

I'd like to add that there is a codelab on developer.android.com for this purpose.

In all required fragments, you define a "next_action" (IDs obviously don't have to be unique) like this:

<action
    android:id="@+id/next_action"
    app:popUpTo="@id/home_dest">
</action>

Then, conditionally, you can set onClickListeners in your code:

view.findViewById<Button>(R.id.navigate_action_button)?.setOnClickListener(
    Navigation.createNavigateOnClickListener(R.id.next_action, null)
)