Shared ScreenModel between screens

[renaudmathieu]

Voyager by default expect that it screens can be stored inside a Bundle. This means both Java Serializable and Parcelable are supported. By default all Voyager Screen is Java Serializable this means that Screen can be restored if all parameters are Java Serializable.

Is there a way to share the same ScreenModel between screens?

[programadorthi]

Well, a ScreenModel is remembered by Compose SlotTable and associated to a Screen. The idea is the same as Android ViewModel. Can you share a ViewModel with two Activities?
So, a hack try to you have a ScreenModel available to two Screen is:

1. Create a Singleton Screen.
2. In both Screen do: val model by SingletonScreen.rememberScreenModel<YourScreenModel>()

I have not tested that but as you can see in the code a remembered ScreenModel is associated to a Screen. So, a Singleton Screen should works

[osrl]

but you can share a viewmodel with two fragments via navhost. it's a pretty common usage.

[renaudmathieu]

I've found a temporary solution using Koin.

1. Add the following dependencies:

implementation("io.insert-koin:koin-core:3.4.3")
implementation("io.insert-koin:koin-compose:1.0.4")

2. Start Koin and define a Single ScreenModel

KoinApplication(application = {
        modules(appModule)
}) {

3. Then you can inject it

val appScreenModel = koinInject<AppScreenModel>()

[osrl]

but this is scoped to entire app. it's never disposed right?

[Ric-AB]

Has anyone found a solution to this?

[osrl]

checkout #217

[DevSrSouza]

I think the main question here is: Where do we will scope it.

1. If you are running Single Activity, and using only one Navigator for the hole app, there is no place to Scope and free de ScreenModel/ViewModel, we could have a be scoped at the Navigator level but it will always stay alive.
2. If you are running Multiple Activities, one per flow, you can use for example Kodein Scoped Injection or Koin.
3. If you are running Single Activity but Nested Navigation for scoping features, in this case, the feat: added support to have navigator scoped ViewModel #217 should be what you are looking for.

[DevSrSouza]

I had add new API for Navigator scoped ScreenModel, checkout, it is available starting from 1.0.0-rc08
#233

Docs: https://voyager.adriel.cafe/screenmodel#navigator-scoped-screenmodel

[osrl]

#217 will still be needed for ViewModels. Do you plan merging it?