I am getting some weird error with the new Compose...

# compose

[Mehdi Haghgoo]

I am getting some weird error with the new Compose Navigation.

NavHost(navController, startDestination = "home"){
        composable("new-item"){NewItem(navController)}
        composable("profile/{name}", listOf(navArgument("name"){type = NavType.StringType}))
        {navBackStackEntry ->
            Profile(navBackStackEntry.arguments?.getString("name").toString())
        }

        composable("home?costName={costName}&costValue={costValue}",
                arguments = listOf(navArgument("costName"){nullable = true}, navArgument("costValue"){type = NavType.IntType; defaultValue = 0})){
            navBackStackEntry ->  Home(navController, navBackStackEntry.arguments?.getString("costName"), navBackStackEntry.arguments?.getInt("costValue"))
        }
    }

//    java.lang.IllegalArgumentException: navigation destination 150924488 is not a direct child of this NavGraph
//    at androidx.navigation.NavGraphNavigator.navigate(NavGraphNavigator.java:66)

[Ian Lake]

home != home?costName={costName}... - those need to match exactly

[Mehdi Haghgoo]

but home?costName is not optional arguments?

[Mehdi Haghgoo]

Sometimes I need to pass it some arguments and sometimes no arguments.

[Ian Lake]

There's no problem with how you're defining home, it is the start destination that isn't matching - the ID generated from the route is based on the whole string

[Mehdi Haghgoo]

Matching them does not seem to help either 😞

NavHost(navController, startDestination = "home?costName=null&costValue=0"){
        composable("new-item"){NewItem(navController)}
        composable("profile/{name}", listOf(navArgument("name"){type = NavType.StringType}))
        {navBackStackEntry ->
            Profile(navBackStackEntry.arguments?.getString("name").toString())
        }

        composable("home?costName={costName}&costValue={costValue}",
                arguments = listOf(navArgument("costName"){nullable = true}, navArgument("costValue"){type = NavType.IntType; defaultValue = 0})){
            navBackStackEntry ->  Home(navController, navBackStackEntry.arguments?.getString("costName"), navBackStackEntry.arguments?.getInt("costValue"))
        }
    }

//    java.lang.IllegalArgumentException: navigation destination -423783418 is not a direct child of this NavGraph

[Ian Lake]

What I mean is that the strings need to match exactly: startDestination="home?costName={costName}&costValue={costValue}"

[Ian Lake]

The start destination is trying to find the composable with the exact same route. It has nothing to do with starting arguments (which aren't supported at the moment - you'll always get only your default values for arguments for the start destination), etc.

[Ian Lake]

In general, the start destination of your app should very much be a unique, recognizable first entry point for users launching your app, which, tbh, doesn't lend itself at all to optional arguments or something that you'd reuse later in your app, but obviously without details on exactly how your app is set up, it is hard to say if that rule of thumb applies here

[Mehdi Haghgoo]

@Ian Lake I agree. I think I should remove parameters for the start destination and instead pass a viewmodel to the composable so that it can save costName and costValue in the NewItem composable for example rather than returning them to home destination, which I intended to do initially.
So, is it a bad idea to use navigation to return some data to a destination in compose like what we were used to in classic Android?

[Ian Lake]

You'd want to use Navigation's API for returning a result, which works perfectly in Compose: https://developer.android.com/guide/navigation/navigation-programmatic#returning_a_result

[Ian Lake]

You should never have been using navigate() for returning a result