Hi folks, In compose multiplatform, suppose on bac...

# compose

[Sunil Kumar]

Hi folks, In compose multiplatform, suppose on back press we need to clear some state data from screen viewModel so that next time screen works properly, how to do that, becoz in android we can use BackHandler for that?, But how to do that kind of stuff in compose multiplatform that works for all platforms?

[Hristijan]

https://exyte.com/blog/jetpack-compose-multiplatform

[Alex Styl]

Same question answered on #C01F2HV7868 https://kotlinlang.slack.com/archives/CJLTWPH7S/p1726177322768589

[Sunil Kumar]

Thanku guys. 🙌

[Stylianos Gakis]

we need to clear some state data from screen viewModel so that next time screen works properly

You shouldn't have to do anything in a BackHandler for this.
You should be getting a brand new ViewModel after you've popped a destination completely and you go back into it.
What are you using for navigation? And how are you grabbing your viewmodel there? Is it scoped properly only to that destination's lifecycle?

[Sunil Kumar]

Exactly, i was also expecting this, but not sure why it didnt happened. Im passing viewmodel in screen route composable and using compose navigation

[Stylianos Gakis]

How are you grabbing the viewmodel then? Where are you calling the function which creates the viewmodel?

[Sunil Kumar]

Directly injecting into screen route method as parameter using koinInject

[Stylianos Gakis]

It'd be best to paste the code here inside your composable<Screen> { ... } function

[Sunil Kumar]

Ok, i will check with this way.
I was doing it like this,

@Composable
fun SearchRoute(
    modifier: Modifier = Modifier,
    searchViewModel: SearchViewModel = koinInject(),
) { ... }

Now u mean, i should do it like this?

composable<Screen> { 
   val searchViewModel: SearchViewModel = koinInject()

   searchScreenNavGraph(searchViewModel)
}

Let me try.

[Stylianos Gakis]

No honestly that should be the same thing, just one thing to confirm. If inside your screen you do

@Composable
fun SearchRoute(
    modifier: Modifier = Modifier,
    searchViewModel: SearchViewModel = koinInject(),
) { 
  LaunchedEffect(searchViewModel) {
    Log.d("searchViewModel", "searchViewModel hashcode:${searchViewModel.hashCode()}")
  }
  ...
}

And you go to that screen, let it print something.
Then go back, pop the backstack so this screen leaves the composition completely.
And then you navigate to this screen again. Is the hashCode printed the same one as before?

[Sunil Kumar]

Yea, thats what i was thinking they should be the same thing.
And i tried hashCode, its coming as same, its weird.

[Stylianos Gakis]

AH!
Do not use koinInject use koinViewModel 😄
I completely missed that

Replace

searchViewModel: SearchViewModel = koinInject(),

with

searchViewModel: SearchViewModel = koinViewModel(),

[Stylianos Gakis]

In your module definition, if you are doing:

module {
 single<SearchViewModel> { SearchViewModel(get()) }
}

Replace with

module {
 viewModel<SearchViewModel> { SearchViewModel(get()) }
}

[Stylianos Gakis]

https://insert-koin.io/docs/quickstart/android-viewmodel

[Sunil Kumar]

Ok, is koinViewModel support available for multiplatform now? In which koin version?

[Sunil Kumar]

I was not able to use it, thats why. Not sure which koin version supports koinViewModel for multiplatform, i will check that

[Sunil Kumar]

Ah, i think i missed koin-compose-viewmodel, i thought koin-compose, include that too

[Stylianos Gakis]

https://github.com/InsertKoinIO/koin/blob/f870a02fd32a2cf1ff8b69406ebf555c26ffe39f[…]l/src/commonMain/kotlin/org/koin/compose/viewmodel/ViewModel.kt 👍

[Sunil Kumar]

Thnx, I was just thinking that koin-compose include viewModel api as well and multiplatform support is not available yet 😀. But just found out there is the separate extension for that.

[agrosner]

Don’t you need to also scope the view model to the backstack entry in. Compose navigation

[agrosner]

at least in hiltViewModel, you need to do hiltViewModel(backstackEntry) to make unique viewmodel per screen instance

[Ian Lake]

The scoping is done automatically for you inside a composable destination since NavHost already sets the LocalViewModelStoreOwner to that destination (and that's the default value for viewModel, etc.)