how to implement Conditional Navigation in navigation architecture components

问题

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.

回答1:

You can add navigation listener inside your activity, and from there navigate to LoginFragment based on your conditions, like this:

findNavController(nav_host_fragment).addOnNavigatedListener { controller, destination ->
        when(destination.id) {
            R.id.HomeFragment-> {
             if(someCondition) {
               //Navigate to LoginFragment
             }

        }
    }

回答2:

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)
       }
   }
   

来源：https://stackoverflow.com/questions/50493988/how-to-implement-conditional-navigation-in-navigation-architecture-components