Asking for opinions: is it preferable to have a sh...

# multiplatform

[Darryl Pierce]

Asking for opinions: is it preferable to have a shared ViewModel or should the ViewModel be platform-specific? My app is currently targeting iOS and Android and using a shared ViewModel based on code from the Kotlin Multiplatform tutorial book from Kodeco.

[Arsildo Murati]

I am sharing viewmodels with kmp native coroutines and kmp observable viewmodel and using a mix of swift ui and compose screens, worked out great so far

[Darryl Pierce]

I think I may be doing something wrong then. How do you share changes to the viewmodel with your top level composables on both platforms? I'm, as I mentioned, using code I borrowed from Kodeco's KMP book and it acts like the state is causing the view model to change which causes the state to change, ad infinitum.

If you look at this class:

https://github.com/mcpierce/variant/blob/feature/issue-8/shared/src/commonMain/kotlin/org/comixedproject/variant/shared/model/VariantViewModel.kt

I used their example to publish changes to the list of links to display:

var onDisplayLinksUpdated: ((List<AcquisitionLink>) -> Unit)? = null
set(value) {
field = value
onDisplayLinksUpdated?.invoke(acquisitionLinks)
}

This class is the root composable on the Android platform, and it subscribes to those changes to update the state variable that is the list of links to display:

https://github.com/mcpierce/variant/blob/feature/issue-8/androidVariant/src/main/java/org/comixedproject/variant/android/ui/RootView.kt


var displayLinks by remember {
mutableStateOf(listOf<AcquisitionLink>())
}

viewModel.onDisplayLinksUpdated = {
displayLinks = it
}

I keep seeing the displays repeatedly updating, even though the display doesn't change itself at all and is responsive to clicks.

Is this the wrong approach?

[Arsildo Murati]

I don't understand exactly what top Composables means exactly 🤔

[Darryl Pierce]

The root compostable function called from MainActivity.

[Arsildo Murati]

are you going full compose multiplatform or using swift ui?

[Darryl Pierce]

SwiftUI but I’ve only done a bit of it so far.

[Arsildo Murati]

Well it really depends on the usecase, but In this case you can probably share the viewmodel and listen to the state and react to it the same way on both platforms

[Arsildo Murati]

As i said I am using native coroutines and observable viewmodel and the logic is pretty much the same on both platforms whilst the ui staying mostly native

[Darryl Pierce]

Can you point me to a good example or tutorial? I’m doing that now but as I mentioned it seems to be looping between view model events causing an update that causes the view model to update, etc.

[Arsildo Murati]

You most likely need to explore your options and try some different approaches and see what works best for you

[Arsildo Murati]

If you plan to use my aproach, https://github.com/rickclephas/KMP-ObservableViewModel

[Darryl Pierce]

Thank you! I’ll take a look.

[Arsildo Murati]

the android part/jvm is pretty much what you are used to already

[Arsildo Murati]

this lib just makes it alot easier to feed the viewmodel to swiftui the same way you feed it to compose using state flows