SingleOf does not generate truly singleton objects

[ksharma-xyz]

Describe the bug
When navigating between screens (ScreenA to ScreenB) that use ViewModelA and ViewModelB, and then switching between dark/light themes, the Repo object injected into ViewModelB is recreated. This behavior occurs despite defining Repo as a singleton in the Koin module. As a result, ViewModelB does not share the same Repo instance as ViewModelA, which breaks the expected singleton behavior. Based on compose multiplatform project.

To Reproduce
Steps to reproduce the behavior:

• Create a module with a interface and it's implementation.

val repoModule = module {
    singleOf(::RealRepo) { bind<Repo>() }
}

• Create two Screen composables and ViewModels and inject the repo in the constructor
  ScreenA / ViewModel A and ScreenB / ViewModel B

class ViewModelA(
    private val repo: Repo,
) : ViewModel() { ...  }

class ViewModelB(
    private val repo: Repo,
) : ViewModel() {  ... }

• Navigate from Screen A to B and then switch between dark / light theme.
• Navigate Back to screen A and then again to Screen B.
• See Error: Notice that ViewModelB has a new repo object created.

Expected behavior
ViewModelB should have the same Repo object as is present inside ViewModelA

Koin module and version:

koin = "4.0.1-Beta1"
io.insert-koin:koin-android
io.insert-koin:koin-compose-viewmodel
io.insert-koin:koin-compose-viewmodel-navigation

Snippet or Sample project to help reproduce
Add a snippet or even a small sample project to help reproduce your case.

Creating viewmodel like this in composable scope.

internal fun NavGraphBuilder.myDestination(navController: NavHostController) {
    composable<ARoute> { backStackEntry ->
        val route = backStackEntry.toRoute<ARoute>()
        val viewModel: ViewModelA = koinViewModel<ViewModelA>()
        ScreenA()
    }
}


internal fun NavGraphBuilder.myDestination(navController: NavHostController) {
    composable<BRoute> { backStackEntry ->
        val route = backStackEntry.toRoute<BRoute>()
        val viewModel: ViewModelB = koinViewModel<ViewModelB>()
        ScreenB()
    }
}


interface Repo {
    fun do()
}

class RealRepo : Repo {

    init {
        println("Repo created $this")
    }

[arnaudgiuliani]

I don't think it's related to Koin here. How do you restart your app/them?

[ksharma-xyz]

In Hilt, if we mark a class as Singleton, then the instance is same as long as the app process is active. It should be same for Koin too? If a configuration change happens, then a new object should not be created.

• Using Koin, the Singleton object is created again when a config change happens.
• Using Hilt, the singleton object truly remains singleton, when config change happens.

Koin	Hilt
Koin_Singleton_NewObjects.mov	Hilt_Singleton.mov

I've created a sample android project to highlight this here: https://github.com/ksharma-xyz/KoinSingletonBug

• main branch - sample using koin
• hilt branch - sample using hilt

[afTrolle]

You are having scope issues, you are creating a koin instance too the activity scope. That's why it's recreated on configuration changes.

Start your koin instance in the Application class instead.

Change MainApplication & KoinApplication.

class MainApplication : Application() {

    override fun onCreate() {
        super.onCreate()

        startKoin {
            modules(
                repoModule,
                viewModelsModule,
            )
            androidContext(this@MainApplication)
        }
    }

} 

And replace with KoinApplication with KoinAndroidContext

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        enableEdgeToEdge()
        setContent {
            val navController = rememberNavController()

            KoinAndroidContext {
            ...
            }
        ...
}

See Docs here
https://insert-koin.io/docs/reference/koin-android/get-instances#using-the-android-context-in-a-definition

[ksharma-xyz]

Thanks! @afTrolle That worked for an android application. Do you have any suggestions for a ComposeMultiplatform Application?

Seems like setting android context in MainApplication using startKoin is not enough, we also need to set it in the org.koin.compose.KoinApplication. Otherwise, the following error occurs:

java.lang.IllegalStateException: Koin context has not been initialized in rememberKoinApplication

startKoin {
    androidContext(this@KrailApplication) // not enough as KoinApplication also expects androidContext.
}

[afTrolle]

Thanks! @afTrolle That worked for an android application. Do you have any suggestions for a ComposeMultiplatform Application?

Seems like setting android context in MainApplication using startKoin is not enough, we also need to set it in the org.koin.compose.KoinApplication. Otherwise, the following error occurs:

java.lang.IllegalStateException: Koin context has not been initialized in rememberKoinApplication

startKoin {

    androidContext(this@KrailApplication) // not enough as KoinApplication also expects androidContext.

}

It might depend on which platform/target we are talking about.

I'm no expert in koin.

But you could probably use previous solution for the others.
Just do a check if Koin is instantiated already otherwise use other solution.

In my iOS code I do similar to android application but call function init function when app starts. But that was just convient because I'm also starting up crashlytics from swift.

[ksharma-xyz]

Any updates on this @arnaudgiuliani. The issue is for Compose Multiplatform.

[arnaudgiuliani]

If you want to start Koin before Compose, you need to use KoinAndroidContext or KoinContext instead of KoinApplication. Else it will try to start a new context.