Hey <@UHAJKUSTU>, WDYT of adding a built-in way of...

# mvikotlin

[Nacho Ruiz Martin]

Hey @Arkadii Ivanov, WDYT of adding a built-in way of mapping states out of the store when using stateFlow extension?

I’ve found that if you map it with:

store.stateFlow.map(::mapper).stateIn(scope, SharingStarted.Eagerly, store.state.mapper())

you fall into the everlasting problem of textfield states.

I’ve been thinking of adding an optional mapping function inside stateFlow. This would help users of MviKotlin + Decompose that want to use Coroutines all the way down.

[Nacho Ruiz Martin]

I’ve copied the source of the stateFlow extension and modified it in my app. It looks like:

fun <State : Any, Model : Any> Store<*, State, *>.stateFlow(mapper: State.() -> Model): StateFlow<Model> =
    StoreStateFlow(store = this, mapper)

private class StoreStateFlow<State : Any, Model : Any>(
    private val store: Store<*, State, *>,
    private val mapper: State.() -> Model,
) : StateFlow<Model> {

    override val value: Model get() = store.state.mapper()
    override val replayCache: List<Model> get() = listOf(store.state.mapper())

    override suspend fun collect(collector: FlowCollector<Model>): Nothing {
        val flow = MutableStateFlow(store.state.mapper())
        val disposable = store.states(observer { flow.value = it.mapper() })

        try {
            flow.collect(collector)
        } finally {
            disposable.dispose()
        }
    }
}

[Nacho Ruiz Martin]

Problem: stateFlow is no longer a variable, but a function.

[Arkadii Ivanov]

WDYT of adding a built-in way of mapping states out of the store when using stateFlow extension?

Technically it's possible, but's not as easy as it may look like. I.e. ideally the value property should be cached to avoid calling the mapper every time.

you fall into the everlasting problem of textfield states

You should use Dispatchers.Main.immediate there as well. E.g. the scope you are passing into stateIn function should be created with Main.immediate dispatcher. And also use Main.immediate when you collect the flow. Then it should work fine.

[Nacho Ruiz Martin]

Oh, didn't know you could also stateIn Dispatchers.Main! I'll try that one. Many thanks.

[Arkadii Ivanov]

I don't think you can, stateIn needs a CoroutineScope. But you can create the scope with Dispatchers.Main.immediate.

[Nacho Ruiz Martin]

Ah, ok that makes even more sense 👍