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How to navigate to deeply nested screen composable from the Activity's onCreate in Jetpack Compose

Suppose I have a notification, that when clicked, launches my app's activity. It's a notification about a message, in a conversation, and so it launches the activity passing the conversationId as an argument. When the activity is launched by that intent from the notification, it should open MessagesScreen, which is a deeply nested screen in the app, passing to it conversationId.
What is the best way to do this in Compose? In the good old Fragments or Activities you just navigated straight to it, but with Compose is a little trickier. The path to the MessagesScreen is as follows:
SplashScreen (checks for authentication) -> HomeScreen (if authenticated) -> ConversationScreen -> MessagesScreen
I can't just navigate straight to MessagesScreen by having the compose's NavController be stored in the Activity, since I need to go through SplashScreen to check for authentication. Also, I don't know the Compose's implication of navigating to a deeply nested component from the Activity's onCreate().
What I currently do is have a field in my global ViewModel called notificationConversationId, that is set on my Activity's onCreate if it was passed by the notification's intent:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val conversationId = intent.getStringExtra("conversation_id") ?: ""
globalViewModel.notificationConversationId = conversationId
// ...
Then, in a LaunchedEffect in my HomeScreen I observe this field, and if it is not empty, I navigate to the MessagesScreen, and set it to an empty string, so the LaunchedEffect is not executed again.
val conversationId = globalViewModel.notificationConversationid
LaunchedEffect(conversationId) {
if (conversationId.isNotEmpty()) {
val path = getMessagespath(conversationId = conversationId)
globalViewModel.notificationConversationId = ""
navController.navigate(path)
}
}
It works, but it is horrendous. Is there a better way to accomplish this in Compose? Thanks in advance.

Why google-iosched can save fragment state while navigating with navigation component

Overall look at the code, I don't understand why it can be done.
https://github.com/google/iosched
from apps/iosched/ui/MainActivity.kt, It initialized NavController and NavHostFragment, but seems that there is no special treatment.
https://github.com/google/iosched/blob/main/mobile/src/main/java/com/google/samples/apps/iosched/ui/MainActivity.kt
val appBarConfiguration = AppBarConfiguration(TOP_LEVEL_DESTINATIONS)
private val TOP_LEVEL_DESTINATIONS = setOf(
R.id.navigation_feed,
R.id.navigation_schedule,
R.id.navigation_map,
R.id.navigation_info,
// R.id.navigation_agenda, comment will not stop saving the statement.
R.id.navigation_codelabs,
R.id.navigation_settings
)
from apps/iosched/ui/AgendaFragment.kt: the most simplest fragment, BindingAdapter method will always init AgendaAdapter(), but It can save the position of RecyclerView after init.
https://github.com/google/iosched/blob/main/mobile/src/main/java/com/google/samples/apps/iosched/ui/agenda/AgendaFragment.kt
Why can it save the State of each fragment?

IOSched depends on Navigation 2.4.1. As per the release notes of Navigation 2.4.0:
The NavController ... has been expanded to support saving and restoring the back stack.
As part of this change, the NavigationUI methods of onNavDestinationSelected(), BottomNavigationView.setupWithNavController() and NavigationView.setupWithNavController() now automatically save and restore the state of popped destinations, enabling support for multiple back stacks without any code changes. When using Navigation with Fragments, this is the recommended way to integrate with multiple back stacks.
And IOSched uses setupWithNavController, which means each tab is automatically going to save and restore its state correctly.
That includes the state of a RecyclerView, which has always supported saving and restoring its position automatically.

Compose navigate to screen that already in backstack

I want to have navigation that looks like this:
-I have three screens: "Login", "Registration", and "Account recovery";
-from each screen, I can navigate to any other;
-when I navigate from the "Login" screen to "Registration" and then return to the "Login" (clicking the button "Go to login"), I want to have the same screen as at the beginning, not a new one.
Now, each time, when I go back to "Login", I get a new screen :(
My NavHost:
val navController = rememberNavController()
NavHost(navController = navController, startDestination = Screens.Login.route) {
composable(route = Screens.Recovery.route) {
RecoveryScreen(navController = navController)
}
composable(route = Screens.Login.route) {
LoginScreen(navController = navController)
}
composable(route = Screens.Registration.route) {
RegistrationScreen(navController = navController)
}
}
Guide me which way to dig?

I am late, but it may help someone check Jetnews sample app in GitHub,
navigate like this
navController.navigate(JetnewsDestinations.HOME_ROUTE) {
// Pop up to the start destination of the graph to
// avoid building up a large stack of destinations
// on the back stack as users select items
popUpTo(navController.graph.findStartDestination().id) {
saveState = true
}
// Avoid multiple copies of the same destination when
// reselecting the same item
launchSingleTop = true
// Restore state when reselecting a previously selected item
restoreState = true
}
this avoid multiple back stack also restore state of previous opened destination

How do you know that it is a new screen? Let me guess, you must be looking at some state of the screen, for example, filled textfields would be empty, scrolled lists would be reset, checkboxes would be reset or something to this effect. You see it does not matter whether you are calling the stuff from the backstack. The thing is, the moment a Composable is no longer visible on screen, it is destroyed, resetting all the state to the default values. That is, it will always be recomposed upon navigation request. What you need here is to store all that state inside a viewmodel. Then, reference the state from the viewmodel itself. Create state variables in the viewmodel with default values, then always reference from the viewmodel itself. This way, upon recomposition, the data would be fetched from the vm, and it will still be the correct data since the vm is not destroyed.

Basic testing NavigationController in Android

I'm currently new to testing, so I decided to start off with some basic stuff.
I handle all my navigations from a DrawerLayout that is connected to an Activity.
So for my testing I launch an ActivityScenarioRule, create a testNavController object and then I set this testNavController to the current view that handles the navigation (The container fragment).
So the test consists on opening the drawer, clicking on menu item(Will navigate to a fragment) and therefore check if navigated to the fragment.
Then I check if that happened, but the testNavController stays on the same destination which is weird because it performs the click, so I decided to check the navController (The real one inside the activity), and it shows me that navigated to the correct fragment.
Here's the needed code:
#LargeTest
#RunWith(AndroidJUnit4::class)
class MapsActivityTest {
#get:Rule
var activityScenarioRule = ActivityScenarioRule(MapsActivity::class.java)
#Test
fun clickOnDrawerMaps_NavigateToAboutAppFragment() {
//Create TestNavHostController
val testNavController = TestNavHostController(ApplicationProvider.getApplicationContext())
UiThreadStatement.runOnUiThread { // This needed because it throws a exception that method addObserver must be called in main thread
testNavController.setGraph(R.navigation.nav_graph)
}
val scenario = activityScenarioRule.scenario
var navcontroller : NavController? = null
scenario.onActivity {mapsActivity ->
navcontroller = mapsActivity.navController //Get the real navController just to debug
mapsActivity.navController = testNavController //Set the test navController
Navigation.setViewNavController(mapsActivity.binding.containerFragment, testNavController)
}
onView(withId(R.id.drawerLayout)).perform(DrawerActions.open()).check(matches(isOpen()))
onView(withId(R.id.aboutAppFragment)).perform(click())
assertThat(testNavController.currentDestination?.id).isEqualTo(R.id.aboutAppFragment)
}
}
In the example they use a Fragment, which they set the fragment.requireView() on the launch of the fragment, but I think it's exactly the same.
What am I doing wrong here?

When you use ActivityScenario (or ActivityScenarioRule), your activity is brought all the way up to the resumed state before any onActivity calls are made. This means that your real NavController has already been created and used when you call setupWithNavController. This is why your call to setViewNavController() has no effect.
For these types of integration tests (where you have a real NavController), you should not use TestNavHostController.
As per the Test Navigation guide, TestNavHostController is designed for unit tests where you do not have any real NavController at all, such as when testing one fragment in isolation.

How to kill all fragments created by a NavHostFragment?

I have 2 navigation files, and in my Activity, 2 fragments. One of the navigations is always shown inside one of the fragments, but I show the other one only when I need it.
The way they're drawn is the always showing fragment is inside a relativeLayout, and the other fragment is inside the same relativeLayout with it's visibility set as gone. When I need the second navigation, I set the visibility to visible and when I don't need it, I set it to gone again.Visually this works well, but what I want to accomplish is that when I don't want the second navigation, I want to completely kill it and redraw it the next time I need it.
What I've done so far was to get a hold of the NavHostFragment used to start the navigation, and when I dont need it anymore, call popBackStack() on it's navController, but it doesn't work:
val navHost: NavHostFragment? = null
fun createSecondNav() {
navHostLogin = NavHostFragment.create(R.navigation.navigation_second)
theFragment.visibility = View.VISIBLE
supportFragmentManager.beginTransaction()
.replace(R.id.theFragment, navHostLogin!!)
.commit()
}
fun killSecondNav() {
theFragment.visibility = View.GONE
navHostLogin?.navController?.popBackStack() // returns false
navHostLogin = null
}
So how can I completely kill the fragments created by the second navHost?

NavController maintains it's own back-stack, independent form the FragmentManager back-stack.
And popBackStack() without arguments only pops that back-stack once:
Attempts to pop the controller's back stack. Analogous to when the user presses the system Back button when the associated navigation host has focus.
While popBackStack(int destinationId, boolean inclusive) reads:
Attempts to pop the controller's back stack back to a specific destination.
destinationId int: The topmost destination to retain
inclusive boolean: Whether the given destination should also be popped.
So this should be:
navController.popBackStack(R.id.startDestination, true)
I'd wonder why even using two NavController, because one can set the graph at run-time with setGraph(NavGraph graph, Bundle startDestinationArgs):
Sets the navigation graph to the specified graph.
Any current navigation graph data (including back stack) will be replaced.