Is there something like `flatMapLatest` that I can...

# coroutines

[Florian]

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]

will it work for you?
firstFlow.filter { condition }.take(1).flatMapLatest { secondFlow }

[Florian]

no I don't think so

[Florian]

my Flow is a property while the condition happens inside the init block

[Giorgos Neokleous]

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]

@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]

I need the Flow as a property

[Florian]

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())
        }

[Florian]

but I want to do this only in the init block

[Florian]

maybe I need to collect inside the init block?

[Florian]

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?

[Florian]

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