I have a launched effect that doesn t seem to trigger a nav

Question

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 · Answer

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 gt 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 · Answer

`if user = null ` is that condition expected Navigate to the login if the `user` is not null

Colton Idle · Answer

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

Alex Vanyo · Answer

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 · Answer

currentUser is a stateFlow ```val currentUser StateFlow lt AppUser gt ``` 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 · Answer

gt 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 · Answer

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 · Answer

gt 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 · Answer

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 · Answer

I wonder if I should just add the initial value hm ``` collectAsState initial = null ```

Colton Idle · Answer

this is a really bad time to be using logcatv2 it just doesn t show logs on app launch lol sob

Colton Idle · Answer

Maybe its because I m routing to a destination in a nested nav graph thinking face

Colton Idle · Answer

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 · Answer

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 · Answer

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

Colton Idle · Answer

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 · Answer

cc < Doris Liu>

rook · Answer

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 · Answer

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

rook · Answer

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 · Answer

Hm I have no idea lol < Alex Vanyo> do you have any idea