Getting a crash when I try to obtain my route via ...

# compose-android

[Ahmed]

Getting a crash when I try to obtain my route via savedStateHandle and toRoute api. More in 🧵

[Ahmed]

If I have the following structure of navigation

navigation<MyGraph> (startDestination = A) {
  composable<A> {
    val vm = hiltViewModel<VMA>()
  }

  composable<B> {
    val vm = hiltViewModel<VMB>()
  }
}

and I navigate via

fun NavController.navigateToMyGraph(myInt: Int) {
  navigate(MyGraph(myInt = myInt))
}

In my VMA I can obtain MyGraph by doing savedStateHandle.toRoute<MyGraph>() and I can obtain myInt as well. But I am unable to do so in VMB and I encounter the following crash.

kotlinx.serialization.MissingFieldException: Fields [myInt] are required for type with serial name '<MY_PACKAGE_NAME>.MyGraph', but they were missing

at kotlinx.serialization.internal.PluginExceptionsKt.throwMissingFieldException(PluginExceptions.kt:20)
at <MY_PACKAGE_NAME>.MyGraph.<init>(Routes.kt:6)
at <MY_PACKAGE_NAME>.MyGraph$$serializer.deserialize(Routes.kt:6)
at <MY_PACKAGE_NAME>.MyGraph$$serializer.deserialize(Routes.kt:6)

What am I doing wrong here or what am i missing?

[Ahmed]

On a side note, this works fine if I specify default values for MyGraph . But the issue is that it defaults to the given value, and I am unable to retrieve the actual myInt .

[Ian Lake]

The only place you should be using toRoute<MyGraph>() is with getBackStackEntry<MyGraph>() or in ViewModels scoped to getBackStackEntry<MyGraph>()

It only accidentally works in A because we pass arguments down the the start destination and you just happen to use the same field name

[Ahmed]

Ah! So I should rather obtain it in composable.

val myGraph = remember(navBackStackEntry) {
  navController.getBackStackEntry<MyGraph>().toRoute<MyGraph>()
}

So, this would be more appropriate. Thanks!

[Ian Lake]

Yep, looks good to me