Hi, what would be a good way to integrate viewMode...

# decompose

[Jan]

Hi, what would be a good way to integrate viewModels to decompose? Right now my approach is as follow e.g:
• I have a Composable: LoginContent
• I have a Component: LoginComponent
• Inside LoginComponent I defined a ViewModel like this:

class LoginComponent(
    componentContext: ComponentContext,
) : ILoginComponent, ComponentContext by componentContext, KoinComponent {

    private val _viewModel: LoginViewModel =
        instanceKeeper.getOrCreate {
            getKoin().get()
        }

    override val uiState: StateFlow<LoginUiState> = _viewModel.uiState

    ...
}

• My LoginViewModel extends InstanceKeeper.Instance and has an own coroutine scope which gets cleared 'onDestroy' and is lazily initiated
• LoginContent/LoginComponent/LoginViewModel is used within a SlotNavigation
So it seems that the lifecycle of the ViewModel is working correctly on Android. E.g. LoginComponent is recreated during orientationChange, but LoginViewModel stays the same. Thats what I want. So good so far.

I am just wondering if thats a valid approach. I mean its working, so its valid, but is there a "better" way to do it? Should I instead retain the Component instead of the ViewModel or is that exactly the as described here? Thanks

[Arkadii Ivanov]

That's the correct way, all good. Components should never be retained, unless the tree is intentionally not tied to an activity/fragment (by default it is) and don't capture the activity context

[Jan]

and what about constructor injection for the viewModel?

E.G. in my RootComponent I have a slot:

class RootComponent:KoinComponent {

...

childSlot(
    source = slotNavigation,
    handleBackButton = true
) { config, componentContext ->
       LoginComponent(
                componentContext = componentContext
                loginViewModel = getKoin().get()
            )
  }

It seems that the ViewModel is then created on each orientationChange when using this way of injection.

So I think I have to use constructor injection in my RootComponentn as well which leads me to the question if its a good approach to put DefaultComponentContext and Components to Koin?

[Arkadii Ivanov]

You should instantiate the ViewModel inside getOrCreate block in your LoginComponent. You can pass a factory to LoginComponent instead, if you want to abstract away the instantiation.

[Jan]

ah, yes. Thats a nicer way ... Thanks