I would be also interested in sharing the same ViewModel instance between a composable (or multiple ...

# koin

[Lukasz Kalnik]

I would be also interested in sharing the same ViewModel instance between a composable (or multiple composables) and host Fragment/Activity.
My use case is that I have click callbacks in the composables which trigger events in the viewmodel. Then host Fragment subscribes to this event to show snackbar or trigger navigation.

[Moritz Post]

You could create a custom Scope and pass in a "session" object so that each view model gets the same instance

[Lukasz Kalnik]

But then every time I navigate away I would have to destroy the scope.

[Moritz Post]

The scope can be given to each view model

[Lukasz Kalnik]

Yes, but I want to have a new viewmodel once I navigate to the same screen with new data

[Moritz Post]

That would mean you create a new "session".

[Moritz Post]

eg if you have screens like A -> B -> C you would create a new shard "session" object when starting A and pass that shared object to B and C

[Lukasz Kalnik]

So then I would need to create/destroy the session as part of my navigation, right?

[Moritz Post]

Actually not as part of the navigation but automatically in your koin module declaration

[Lukasz Kalnik]

So I just have to do getKoin().createScope()? But when will the session be finished? Will it be automatically finished when I leave the starting fragment?

[Moritz Post]

In that case that would be up to the screen/ViewModel that the session is tied to

[Moritz Post]

Example:

[Lukasz Kalnik]

Ok, that sounds like a good idea to try out.

[Moritz Post]

you create a module with a Session

private val myModule = module {
        scope<Session> {
            scoped { MySession() }
        }
    }

[Moritz Post]

and another which would create your ViewModels:

private var mySessionScope: Scope? = null
    private val viewModelModule = module {
        viewModel {
            mySessionScope = getKoin().createScope<Session>()
            with(requireNotNull(mySessionScope)) {
                ScreenAViewModel(get(), get()).apply {
                    addCloseable { close() }
                }
            }
        }
        viewModel {
            with(requireNotNull(mySessionScope)) {
                ScreenBViewModel(get())
            }
        }
        viewModel {
            with(requireNotNull(mySessionScope)) {
                ScreenCViewModel(get())
            }
        }
    }

[Moritz Post]

Here you can saee that ScreenA is used to close the mySessionScope scope

[Moritz Post]

the get() calls would be able to resolve the shared MySession.

[Lukasz Kalnik]

Interesting, I didn't see that addCloseable before...

[Moritz Post]

That is from androidx.lifecycle.ViewModel

[Moritz Post]

it would than be able to close the session

[Moritz Post]

The solution is not 100% nice because the sessionScope is held in a separate var instead of getting from the koin object each time.

[Lukasz Kalnik]

I see, that's new in 2.5.0

[Lukasz Kalnik]

Thanks for your suggestions, do you know any resource/article which goes in more depth into scoped viewmodels in Koin?
I find that the documentation is missing some of the more specific use cases.

[Moritz Post]

yeah i agree. i pieced it together from the docs and various repos i think.

[Moritz Post]

no immediate pointers

[Lukasz Kalnik]

Ok, thanks so much for your help, this is really cool!

[Moritz Post]

you are welcome. Good Luck.