Hi, I have this code in CommonMain: ```//CommonMai...

# multiplatform

[Jacek]

Hi, I have this code in CommonMain:

//CommonMain
LaunchedEffect(true) {
        viewModel.effect.collect { effect ->
            when (effect) {
                is ConnectingContract.Effect.Error -> {
                    snackbarHostState.showSnackbar(
                        message = "Error occured",
                    )
                }
            }
        }
    }

I want to change hardcoded text to resource using moko library. Unfortunately, I cannot use the fun stringResources() in LaunchedEffect, nor do I have access to Context.
How to achieve this?

I have prepared an expect class Strings which in the Android implementation takes context.

expect class Strings {
    fun stringResource(string: StringResource) : String
}
actual class Strings(private val activity: Context) {
    actual fun stringResource(string: StringResource): String {
        return string.getString(activity)
    }
}

But I have to pass it to every screen...

// Android Main
val context = LocalContext.current
val strings = getKoin().get<Strings> {
    parametersOf(context)
}
ConnectingScreen(
    viewModel = koinViewModel(),
    strings
)

[jamshedalamqaderi]

I'm doing it like this in commonMain without any expect actual function
MR.strings.hellow.localized()

[Jacek]

When I try to use localized() I get an error while building Unresolved reference: localized
Under localized() is this code:

package dev.icerock.moko.resources.desc
actual data class ResourceStringDesc actual constructor(
    val stringRes: StringResource
) : StringDesc, Parcelable {

    override fun localized(): String = stringRes.localized(
        locale = StringDesc.localeType.currentLocale
    )
}

[jamshedalamqaderi]

because localized() is composable function

[Jacek]

So you cannot called it from LaunchedEffect

[jamshedalamqaderi]

nope

[Vlad]

Then call it a line before the LaunchedEffect

[Vlad]

And in general if you want some OOP to be used in the Compose tree you don't need to pass it everywhere, there are compose way to do it - CompositionLocal.

[Jacek]

I cannot call stringResurce(string: StringDesc) a line before the LaunchedEffect bacause this StringDesc i'm getting from LaunchedEffect

Yes, I've heard of CompositionLocal but I don't know how to use it yet 🙂

[Vlad]

val LocalAppResourcesProvider = staticCompositionLocalOf<ResourcesProvider?> {
    null
}

You just declare anything as CompositionLocal, here ResourceProvider my class.
Somewhere on top of the tree you initialize the actual value (if it can't be initialized at the declaration time).

val resourcesProvider: ResourcesProvider = provideResourceProvider()

CompositionLocalProvider(LocalAppResourcesProvider provides resourcesProvider) {
  MyApp()
}

And anywhere down the tree you can access it as simple as:

val resourrsesProvided LocalAppResourcesProvider.current ?: error("App resources provider is not provided for local")

Adding a little bit sugar we can create shortcut to the LocalAppResourcesProvider.current
via defining object:

object AppRes {

    val provider: ResourcesProvider
        @Composable
        get() = LocalAppResourcesProvider.current ?: error("App resources provider is not provided for local")
}

And now I can access it anywhere in the app as simple as AppRes.provider.getString()
Even further, we can go more with the Compose way and create our own Composable function to fetch the resource:

@Composable
fun stringResource(stringToken: StringTokens): String {
    return AppRes.provider.getString(stringToken)
}

And now we have setup to fetch the strings which is fully incapsulates logic how exactly the string is fetched

[Vlad]

As for you exact question, I am not sure why you can prefetch resource before LaunchedEffect. What is your StringDesc? Are variations of it know at compile time?

[Jacek]

// commonMain - no context
LaunchedEffect(true) {
    viewModel.effect.collect { effect ->
        when (effect) {
            ConnectingContract.Effect.AutoNavigateForward -> navigateToApp()
            is ConnectingContract.Effect.ErrorDesc -> {
                val msg: StringDesc = effect.msg
                val msgString: String = strings.stringResource(msg)
                snackbarHostState.showSnackbar(msgString)
            }
        }
    }
}

For this reason, StringDesc is passed as the Effect argument of viewModel. StringDesc is a cross-platform variant of StringResource.
To make a String from StringDesc, in Android I have to use the current activity context (to change the language)

With CompositionLocal I created:

val LocalStrings = staticCompositionLocalOf<Strings?> { null }

I initialize this in Activity

val context = LocalContext.current
CompositionLocalProvider(LocalStrings provides Strings(context)) {
    App()
}

Then I can use it like

val strings = LocalStrings.current ?: throw Exception()

Nice.. I don't like having to throw an exception when null, but maybe I'll come up with something

Thanks!

[Vlad]

Throwing exception is absolutely normal.
It is complete developer error to not provide it.

[Vlad]

Why you collecting the effect inside LaunchedEffect?

[Vlad]

That is your problem not?
Collect it before. Extract and get StringResoruce. Launch effect. Pass the extracted resource to snackbar

[Jacek]

I'm collecting Channel<Effect> wchich has to be collected in coroutine scope.. so I can't get stringresource out of coroutine scope.
Collecting effects inside LaunchedEffect is a normal thing in MVI

[alex009]

to read string resource on android you should use Context, on ios nothing required. So, to use in commonMain with Compose string resource inside Effect you can:
1. declare expect

expect class ResourceReader {
    fun get(resource: StringResource): String
}

@Composable
expect fun getResourceReader(): ResourceReader

2. implement actual for android:

actual class ResourceReader(private val context: Context) {
    actual fun get(resource: StringResource): String {
        return resource.getString(context)
    }
}

@Composable
actual fun getResourceReader(): ResourceReader {
    val context: Context = LocalContext.current
    return remember(context) { ResourceReader(context) }
}

3. implement actual for iOS:

actual class ResourceReader {
    actual fun get(resource: StringResource): String {
        return resource.localize()
    }
}

@Composable
actual fun getResourceReader(): ResourceReader {
    return remember { ResourceReader() }
}

Then you can do in commonMain:

val resourceReader = getResourceReader()

LaunchedEffect(true) {
        viewModel.effect.collect { effect ->
            when (effect) {
                is ConnectingContract.Effect.Error -> {
                    snackbarHostState.showSnackbar(
                        message = resourceReader.get(effect.resource),
                    )
                }
            }
        }
    }