Ist es möglich, startDestination bedingt mit der Android-Navigationsarchitekturkomponente (Android Jetpack) festzulegen?

ich benutze Navigation aus Android-Jetpack um zwischen Bildschirmen zu navigieren. Jetzt möchte ich startDestination dynamisch setzen.

Ich habe eine Aktivität namens MainActivity und zwei Fragmente, FragmentA und FragmentB.

var isAllSetUp : Boolean = // It is dynamic and I’m getting this from Preferences.

    If(isAllSetUp)
    {
     // show FragmentA
    }
    else
    {
     //show FragmentB
    }

Ich möchte den obigen Fluss mithilfe der Navigationsarchitekturkomponente festlegen. Derzeit habe ich startDestionation wie unten verwendet, aber es erfüllt meine Anforderung nicht.

<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/lrf_navigation"
   app:startDestination="@id/fragmentA">

   <fragment
       android:id="@+id/fragmentA"
       android:name="com.mindinventory.FragmentA"
       android:label="fragment_a"
       tools:layout="@layout/fragment_a" />
</navigation>

Ist es möglich, startDestination unter Verwendung der Android-Navigationsarchitekturkomponente bedingt festzulegen?

Finally, I got a solution to my query…

Put below code in onCreate() method of Activity.

Kotlin code

val navHostFragment = (supportFragmentManager.findFragmentById(R.id.home_nav_fragment) as NavHostFragment)
val inflater = navHostFragment.navController.navInflater
val graph = inflater.inflate(R.navigation.nav_main)
//graph.addArgument("argument", NavArgument)
graph.setStartDestination(R.id.fragment1)
//or
//graph.setStartDestination(R.id.fragment2)

navHostFragment.navController.graph = graph

Java code

NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.home_nav_fragment);  // Hostfragment
NavInflater inflater = navHostFragment.getNavController().getNavInflater();
NavGraph graph = inflater.inflate(R.navigation.nav_main);
//graph.addArgument("argument", NavArgument)
graph.setStartDestination(R.id.fragment1);

navHostFragment.getNavController().setGraph(graph);
navHostFragment.getNavController().getGraph().setDefaultArguments(getIntent().getExtras());


NavigationView navigationView = findViewById(R.id.navigationView);
NavigationUI.setupWithNavController(navigationView, navHostFragment.getNavController());

Additional Info

As @artnest suggested, remove the app:navGraph attribute from the layout. It would look something like this after removal

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/home_nav_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true" />

</FrameLayout>

In the case of a fragment tag used instead of FragmentContainerView, the above changes remain the same

Some of the APIs have changed, are unavailable or are not necessary since Akash’s answer. It’s a bit simpler now.

MainActivity.java:

@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  NavHostFragment navHost = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.fragment_main_nav_host);
  NavController navController = navHost.getNavController();

  NavInflater navInflater = navController.getNavInflater();
  NavGraph graph = navInflater.inflate(R.navigation.navigation_main);

  if (false) {
    graph.setStartDestination(R.id.oneFragment);
  } else {
    graph.setStartDestination(R.id.twoFragment);
  }

  navController.setGraph(graph);
}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
  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:layout_width="match_parent"
  android:layout_height="match_parent"
  tools:context=".MainActivity">

  <!-- Following line omitted inside <fragment> -->
  <!-- app:navGraph="@navigation/navigation_main" -->
  <fragment
    android:id="@+id/fragment_main_nav_host"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:name="androidx.navigation.fragment.NavHostFragment"
  />

</androidx.constraintlayout.widget.ConstraintLayout>

navigation_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<!-- Following line omitted inside <navigation>-->
<!-- app:startDestination="@id/oneFragment" -->
<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/navigation_main"
  >

  <fragment
    android:id="@+id/oneFragment"
    android:name="com.apponymous.apponymous.OneFragment"
    android:label="fragment_one"
    tools:layout="@layout/fragment_one"/>
  <fragment
    android:id="@+id/twoFragment"
    android:name="com.apponymous.apponymous.TwoFragment"
    android:label="fragment_two"
    tools:layout="@layout/fragment_two"/>
</navigation>

This can be done with navigation action. Because fragmentA is your start destination, so define an action in fragmentA.

Note these two fields:
app:popUpToInclusive="true" app:popUpTo="@id/fragmentA"

<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/lrf_navigation"
   app:startDestination="@id/fragmentA">

   <fragment
       android:id="@+id/fragmentA"
       android:name="com.mindinventory.FragmentA"
       android:label="fragment_a"
       tools:layout="@layout/fragment_a">

    <action android:id="@+id/action_a_to_b"
            app:destination="@id/fragmentB"
            app:popUpToInclusive="true"
            app:popUpTo="@id/fragmentA"/>
   <fragment>

   <fragment
       android:id="@+id/fragmentB"
       android:name="com.mindinventory.FragmentB"
       android:label="fragment_b"
       tools:layout="@layout/fragment_b"/>
</navigation>

When your MainActivity started, just do the navigation with action id, it will remove fragmentA in the stack, and jump to fragmentB. Seemingly, fragmentB is your start destination.

if(!isAllSetUp)
{
  // FragmentB
  navController.navigate(R.id.action_a_to_b)
}

this is not an answer but Just a replication of @Akash Patel answer in more clean and clear way

// in your MainActivity
navController = findNavController(R.id.nav_host_fragment)
val graph = navController.navInflater.inflate(R.navigation.nav_graph)
if (Authentication.checkUserLoggedIn()) {
      graph.startDestination = R.id.homeFragment
} else {
      graph.startDestination = R.id.loginFragment
}
navController.graph = graph

You can set your starting destination programmatically, however, most of the time your starting logic will consult some remote endpoint. If you don’t show anything on screen your UI will look bad.

What I do is always show a Splash screen. It will determine which is the next Screen to Show.

For instance, in the picture above you can ask in the Splash Screen State if there is a saved LoginToken. In case it’s empty then you navigate to the Login Screen.

Once the Login Screen is done, then you analyze the result save the Token and navigate to your Next Fragment Home Screen.

When the Back Button is Pressed in the Home Screen, you will send back a Result message to the Splash Screen that indicates it to finish the App.

To pop 1 Fragment back and navigate to another you can use the following code:

val nextDestination = if (loginSuccess) {
        R.id.action_Dashboard
    } else {
        R.id.action_NotAuthorized
    }

val options = NavOptions.Builder()
        .setPopUpTo(R.id.loginParentFragment, true)
        .build()

findNavController().navigate(nextDestination, null, options)

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    setSupportActionBar(binding.toolbar)

    val navHostFragment =
        supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
    navController = navHostFragment.navController
    val inflater = navHostFragment.navController.navInflater
    val graph = inflater.inflate(R.navigation.nav_graph)

    // set initial fragment (home or login based on authorization status)
    lifecycleScope.launchWhenCreated {
        viewModel.isAuthorized.collect { isAuthorized ->
            graph.setStartDestination(
                if (isAuthorized) {
                    R.id.homeFragment
                } else {
                    R.id.loginFragment
                }
            )
            navHostFragment.navController.graph = graph
        }
    }
    ...

And it’s very important to remove app:navGraph from androidx.fragment.app.FragmentContainerView of activity layout:

<androidx.fragment.app.FragmentContainerView
    android:id="@+id/nav_host_fragment"
    android:name="androidx.navigation.fragment.NavHostFragment"
    android:layout_width="0dp"
    android:layout_height="0dp"
    app:defaultNavHost="true"
    app:layout_constraintBottom_toTopOf="@id/bottom_navigation_view"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

and then you can remove app:startDestination="@id/homeFragment" from nav_graph.xml (cause it has no any effect anymore)