Hi, I'm moving my ViewModels to a shared module. A...

# koin

[Osman Saral]

Hi, I'm moving my ViewModels to a shared module. And I'm going to use KMMViewModel as base class (which also extends from androidx ViewModel)
Are there any difference between viewModelOf and factoryOf in terms of implementation? I couldn't see any difference when I looked at the source code. But I couldn't understand why viewModelOf exists in the first place, if they're the same

[Marcello Galhardo]

viewModelOf will be wired with a ViewModelProvider when you use the correct viewModel function to get an instance (either with Compose or not; scoping in the ViewModelStore).

For example: if you retrieve a viewModel 3 times in an Activity, you will receive the same instance.

If you use factoryOf , each call will return a new instance - in the previous example, you would get 3 newly created objects.

[Marcello Galhardo]

Please, refer to the Koin docs to better understand:
• Defining a Factory: https://insert-koin.io/docs/reference/koin-core/definitions#defining-a-factory
• Injecting your ViewModel: https://insert-koin.io/docs/reference/koin-android/viewmodel/#injecting-your-viewmodel

[Marcello Galhardo]

You might also want to learn more about how ViewModel works on Android. Please see the official docs here: https://developer.android.com/topic/libraries/architecture/viewmodel#lifecycle

[Osman Saral]

Hi, I surely know how ViewModel works. Thanks 🙂 I wasn't aware that my question made me look like a beginner 😅 It's okay though.
I'm already resolving the dependency with getViewModel from compose. Is it the resolving the dependency that wires the ViewModel with a ViewModelProvider or is it defining the dependency.

I mean, are those differ:
viewModelOf -> getViewModel
factoryOf -> getViewModel

If they do, can you show me how viewModelOf wires with a ViewModelProvider in the source code? Just for educational purposes 😊 (Cuz, the Module.viewModel function in ModuleExt.kt only calls the factory function)

[Marcello Galhardo]

viewModelOf only accepts ViewModel, factoryOf accepts Any?. Scope wise, you are correct. Thanks for pointing it out.

The ViewModelProvider wiring happens here.

KoinViewModelFactory doesn’t seem to check how the viewModel was wired. That is a design flaw IMO.

Koin should:
(1) Only plug ViewModel dependencies declared with `viewModelOf`/`viewModel` in a KoinViewModelProvider.
(2) Koin should have an actual “view model scope”, where dependencies can be safely scoped during the life time of a view model. Right now, that doesn’t seem to be possible.
(3) KoinViewModelFactory should ensure the contract: only viewModelOf dependencies can be provided.

That should ensure improved safety and better memory scoping for dependencies that aren’t reused between view models.

What do you think @arnaud.giuliani?

[arnaud.giuliani]

Yep interesting @Marcello Galhardo
about injecting ViewModel type, viewModel viewModelOf keywords and `by viewModel()`functions are checking for VM types. But it might be open, to let you inject on an interface

[arnaud.giuliani]

I believe it's quite limited about ViewModel injection scope, as finally for example injecting factory instances into ViewModel those instances will follow the VM

[arnaud.giuliani]

regarding KMP side, you should use factory on native side and viewModel on android side, to let this last wire on Android lifecycle

[arnaud.giuliani]

but else yes, there is interesting improvements to bring around VM

[Osman Saral]

@arnaud.giuliani as @Marcello Galhardo confirmed, there is no difference between viewModelOf and factoryOf when I resolve the dependency using getViewModel Doesn't this mean I don't have to use viewModelOf on the Android side? I wanted to declare dependencies on the shared module with factoryOf so I don't have to declare dependencies twice for iOS and Android side. Since I resolve the dependency using the getViewModel on the Android side, it should be fine to use factoryOf

[arnaud.giuliani]

viewModel keyword is behind the scene a Factory. But yeah, improvements should help about that later 👍