Is there something like `flatMapLatest` that I can trigger e kotlinlang #coroutines

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Title

Florian

12/17/2020, 7:58 AM

Is there something like

flatMapLatest

that I can trigger explicitly and only once? I want to switch a Flow to another Flow if a certain condition is met

bezrukov

12/17/2020, 8:49 AM

will it work for you?

firstFlow.filter { condition }.take(1).flatMapLatest { secondFlow }

☝️ 1

Florian

12/17/2020, 9:09 AM

no I don't think so

my Flow is a property while the condition happens inside the

init

block

Giorgos Neokleous

12/17/2020, 9:15 AM

Can you not wrap your emissions into an Either? You can do a homemade either or pull down arrow and use it. You can wrap your emissions into Either left or right based on your condition and unwrapped it on the collection of the flow

wasyl

12/17/2020, 10:10 AM

@Florian Do you mean something like this?

@Test
fun `switching flows`() {
    val condition = MutableStateFlow(false)
    val firstFlow = flow {
        var i = 0
        while (true) {
            emit("original: ${i++}")
            delay(10)
        }
    }
    val secondFlow = flow {
        var i = 0
        while (true) {
            emit("modified: ${i++}")
            delay(10)
        }
    }

    runBlocking {
        val job = launch {
            condition
                .flatMapLatest { switched -> if (switched) secondFlow else firstFlow }
                .collect { println(it) }
        }

        delay(100)
        condition.value = true
        delay(200)
        job.cancel()
    }
}

Florian

12/17/2020, 5:27 PM

I need the Flow as a property

this s my current code:

private val chatMessagesHistoryFlow = chat.asFlow()
        .flatMapLatest { chat ->
            chat?.let {
                chatRepository.getChatMessagesHistory(it).cachedIn(viewModelScope)
            } ?: emptyFlow()
        }.catch { t ->
            showErrorMessage(t.localizedMessage ?: "Message couldn't be loaded")
            emit(PagingData.empty())
        }

but I want to do this only in the

init

block

maybe I need to collect inside the

init

block?

viewModelScope.launch {
    searchingForExistingDirectChat?.join()
    chat.value?.let { chat ->
        chatRepository.getChatMessagesHistory(chat).cachedIn(viewModelScope)
            .catch { t ->
                showErrorMessage(t.localizedMessage ?: "Messages couldn't be loaded")
                emit(PagingData.empty())
            }
            .collect { 
                   chatMessagesHistoryChannel.send(it)
            }
    }
}

Does this make sense?

is there something else than a channel where I could put the collected values into?

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