I have a launched effect that doesn't seem to trig...

# compose

[Colton Idle]

I have a launched effect that doesn't seem to trigger a nav event like 0.1% of the time during app startup. My thought is that it's just some race condition, but if anyone is familiar with compose-nav and launchedEffects wants to take a look at my scenario I'd appreciate it.

Short sample code in thread

[Colton Idle]

Essentially I have my AppRouter (compose nav host) at the root of my project, but I also have an artifical screen for branding (not my choice. my product team forced me to build it). I think my issue happens because of the way I implemented the artificial splash screen.

Box(modifier = Modifier.fillMaxSize()) {
  Box(modifier = Modifier.align(Alignment.Center)) {
    AppRouter(navController)
  }
  // This is my splash screen
  AnimatedVisibility(
      vm.appState.showSplashScreen,
      enter = EnterTransition.None,
      exit = fadeOut()) {
    Box(
        modifier = Modifier.fillMaxSize(),
        contentAlignment = Alignment.Center) { ArtificialSplashScreen() }
  }
}

Inside of my app router, I do a check around most screens to see if the user is logged out. If so then I navigate to the login screen via a launchedEffect.

composable(Screen.Home.route) {
  RequireSignedInUser(navController) {
    HomeScreen()
  }
}

@Composable
fun RequireSignedInUser(
    navController: NavController,
    content: @Composable () -> Unit
) {

  val user by appState.currentUser.collectAsState()

  if (user == null) {
    LaunchedEffect(Unit) { navController.navigate(route = Screen.Login.route) }

This works 99.9% of the time but it seems like sometimes the launchedEffect isn't triggered (either that or the navigate call is failing somehow?). I can repro this... just supppppper infrequently but I do have users complaining. This only seems to happen on fresh installs (user not logged in) Any thoughts?

[Alex Vanyo]

if (user != null) is that condition expected? Navigate to the login if the user is not null?

[Colton Idle]

Whoops sorry. Copy pasta error. That should say if (user == null). Updating now

[Alex Vanyo]

That looks right, so I’m wondering how currentUser gets updated. What is the default value, and does it end up being null in the case where the expected navigate doesn’t happen?

For a race condition like this, my instinct is that currentUser is updated multiple times in short succession, and you can’t rely on any intermediate values being received and acted upon by the LaunchedEffect

[Colton Idle]

currentUser is a stateFlow.

val currentUser: StateFlow<AppUser?>

One thing to add that I should've said already, is that the user check if it fails... it loads the content(). But the content never loads. It's just a blank screen. Hence why I think it does make it to the launchedEffect, but it just doesn't get called, or navigate doesn't get called?

if (user == null) {
    LaunchedEffect(Unit) { navController.navigate(route = Screen.Login.route) }
} else {
  content()
}

[Colton Idle]

and you can’t rely on any intermediate values being received and acted upon by the LaunchedEffect

This statement definitely has me questioning my implementation. hm...

[Colton Idle]

Makes no sense how I install the app and it's literally just blank. I wish I could force a LaunchEffect to be called or something.

[Alex Vanyo]

could force a LaunchEffect to be called

The keys for your LaunchedEffect would be the way to restart the effect, if the keys change. So the current key of Unit implies that it’d only call navigate the first time the user is null and that composable is present.

So maybe some other place is calling navigate right after this effect navigates to Login? You might want to log all of your navigate calls, and see if the order and which ones are happening are what you’d expect.

[Colton Idle]

Yeah. What's difficult is that this doesn't repro easily. Thanks for the sanity check though @Alex Vanyo looks like there is something wonky there.

[Colton Idle]

I wonder if I should just add the initial value. hm

.collectAsState(initial = null)

[Colton Idle]

this is a really bad time to be using logcatv2. it just doesn't show logs on app launch. lol 😭

[Colton Idle]

Maybe its because I'm routing to a destination in a nested nav graph 🤔

[Colton Idle]

Finally able to repro with additional logging

16:22:25.521 5362-5362/? E/ME: RequireSignedInUser recomposed
16:22:25.521 5362-5362/? E/ME: nav to sign up
16:22:25.581 5362-5362/? E/ME: RequireSignedInUser recomposed
16:22:25.581 5362-5362/? E/ME: nav to sign up
16:22:25.748 5362-5362/? E/ME: RequireSignedInUser recomposed
16:22:25.748 5362-5362/? E/ME: nav to sign up
16:22:25.910 5362-5362/? E/ME: RequireSignedInUser recomposed
16:22:25.910 5362-5362/? E/ME: nav to sign up
16:22:25.946 5362-5362/? E/ME: RequireSignedInUser recomposed
16:22:25.946 5362-5362/? E/ME: nav to sign up
16:22:26.276 5362-5362/? E/ME: RequireSignedInUser recomposed
16:22:26.276 5362-5362/? E/ME: nav to sign up

looks like it tried to nav 6 times in a second. getting closer...

[Colton Idle]

to force it to repro I tried to just put a repeat {} block inside of my

fun RequireSignedInUser(

with no luck. still doesn't' repro easily.

[Colton Idle]

ALright. so it only seems to be happening in release builds... the story continues

[Colton Idle]

Update: It seems that if I add some opacity to my background color of my splash screen then the issue goes away? I wonder if this is somehow related to

https://issuetracker.google.com/issues/192993290

[jossiwolf]

cc @Doris Liu

[rook]

I’m curious as to why the navigation is wrapped in a LaunchedEffect . navigate is not a suspend and there’s no reason to delay the navigation until recomposition is completed.

[Colton Idle]

I think it's because I only want it to be called once?

[rook]

Once the log in completes, won’t this be recomposed with a non-null user? That means that the null-user branch is dead for the rest of the lifetime of the composable.

[Colton Idle]

Hm. I have no idea. lol. @Alex Vanyo do you have any idea?