runtime-saveable: supports tvos and watchos

[hoc081098]

Currently, this modules supports android, jvm, js, ios and macos.
Please support tvos and watchos.

[mazunin-v-jb]

Hello, thanks for the issue!
I'll pass it on to the team.

[dima-avdeev-jb]

For now, runtime-saveable have a sence only for Android. For other platform it works the same as remember. So, you can create your own expect fun myRememberSaveable(...) withactual fun myRememberSaveable(...) = remember(...) on all platforms and only one real implementation on androidMain sourceSet: actual fun myRememberSaveable() = rememberSaveable(...)

[hoc081098]

For now, runtime-saveable have a sence only for Android. For other platform it works the same as remember. So, you can create your own expect fun myRememberSaveable(...) withactual fun myRememberSaveable(...) = remember(...) on all platforms and only one real implementation on androidMain sourceSet: actual fun myRememberSaveable() = rememberSaveable(...)

Thanks for your reply.
Imo, using rememberSavable() with rememberSaveableStateHolder() is useful in navigation pattern.
It allows state of a composable can be saved and restored (via Bundle on Android and in-memory on other platforms).

I cannot achieve that by using remember and rememberSaveableStateHolder

[hoc081098]

Originally posted by @syt0r in #1932 (comment)

I did some investigation and looks like rememberSaveable actually works, but you need to implement additional thing to make it work, it's just that android's navigation library already has it implemented underneath. Also on desktop serialization is not really is necessary since everything is stored in memory

To make it work you need to create instance of SaveableStateHolder with rememberSaveableStateHolder() and wrap you navigation destinations with stateHolder.SaveableStateProvider(stringKey) { content }, it will assosiate your content with key and save data for specific destinations, then when removing destination you just need to invoke SaveableStateHolder.removeState(key)

Here is snippet of what I did in my project:

interface MultiplatformMainNavigationState : MainNavigationState {
    val currentDestination: State<MainDestination>
    val stateHolder: SaveableStateHolder
}

@Composable
fun MultiplatformMainNavigation(
    state: MainNavigationState
) {

    state as MultiplatformMainNavigationState

    val destination = state.currentDestination.value

    state.stateHolder.SaveableStateProvider(destination.toString()) {
        when (destination) {
            MainDestination.Home -> {
                val homeNavigationState = rememberHomeNavigationState()
                HomeScreen(
                    viewModel = getMultiplatformViewModel(),
                    mainNavigationState = state,
                    homeNavigationState = homeNavigationState
                )
            }
            MainDestination.About -> {
                AboutScreen(
                    mainNavigationState = state,
                    viewModel = getMultiplatformViewModel()
                )
            }
            // ...others
        }
    }

}

@Composable
fun rememberMultiplatformMainNavigationState(): MainNavigationState {
    val stack = remember { mutableStateOf<List<MainDestination>>(listOf(MainDestination.Home)) }
    val currentDestinationState = remember { derivedStateOf { stack.value.last() } }

    val stateHolder = rememberSaveableStateHolder()

    return remember {
        object : MultiplatformMainNavigationState {

            override val currentDestination = currentDestinationState
            override val stateHolder: SaveableStateHolder = stateHolder

            override fun navigateBack() {
                val lastItem = stack.value.last()
                stack.value = stack.value.dropLast(1)
                stateHolder.removeState(lastItem.toString())
            }

            override fun popUpToHome() {
                val itemsToRemove = stack.value.drop(1)
                stack.value = stack.value.take(1)
                itemsToRemove.forEach { stateHolder.removeState(it) }
            }

            override fun navigate(destination: MainDestination) {
                stack.value = stack.value.plus(destination)
            }

        }
    }
}

[hoc081098]

Closed by #3899

[okushnikov]

Please check the following ticket on YouTrack for follow-ups to this issue. GitHub issues will be closed in the coming weeks.