I'm working on an Android app, and in my VM I have...

# coroutines

[Colton Idle]

I'm working on an Android app, and in my VM I have an init {} block with 3 separate "inifinite" collect {} calls.

viewModelScope.launch {
launch { service.flow1().collect { } }
launch { service.flow2(NEED an id FROM flow 1).collect { } }
launch { service.flow3(NEED an id FROM flow 1).collect { } }
}

What would be the best way to do something like that?

[ephemient]

is your intention something along these lines?

service.flow1().mapLatest { id ->
    coroutineScope {
        service.flow2(id).launchIn(this)
        service.flow3(id).launchIn(this)
    }
}.buffer(0).launchIn(viewModelScope)

which will re-start flow2, flow3 with each id from flow1. (or else what do you expect to happen before an id is available, or after a new value arrives?)

[Colton Idle]

hm. its close.

My "issue" is that flow1() will called a bunch, but the id I need will likely never change, but I need that id first so I can call flow2 and flow3, but flow1 still needs to do a bunch of work.

I think a really simple (but inefficient solution to my problem would be this.

viewModelScope.launch {
    val initialValue = service.flow1().first().someProperty
    launch { service.flow1().collect { //update UI with changes } }
    launch { service.flow2(initialValue).collect { //update UI with changes} }
    launch { service.flow3(initialValue).collect { //update UI with changes} }
}

[Colton Idle]

So why I think

service.flow1().mapLatest { id ->
    coroutineScope {
        service.flow2(id).launchIn(this)
        service.flow3(id).launchIn(this)
    }
}.buffer(0).launchIn(viewModelScope)

wouldn't work is because I don't know where I would do the //update UI with changes for flow1() since the result of Flow1 is a complex model, where I just need one property from that complex model to start flow2 and flow3.

[Francesc]

you can convert your flow into a shared flow after you map it to the id, then use that shared flow to drive your flow2 and flow3, something like this

val idFlow = flow1.map { value ->
            // do whatever processing you need with value here
            value.id
        }.distinctUntilChanged()
            .shareIn(viewModelScope, SharingStarted.Eagerly)

        idFlow.flatMapLatest { id ->
            flow2(id)
        }.onEach { value -> 
            // handle value
        }.launchIn(viewModelScope)

        idFlow.flatMapLatest { id ->
            flow3(id)
        }.onEach { value ->
            // handle value
        }.launchIn(viewModelScope)

[Francesc]

another option is to make your flow shared and then launch 3 collectors on that

val sharedFlow = flow1
    .shareIn(viewModelScope, SharingStarted.Eagerly)

sharedFlow
.onEach { flow1Value ->
    // handle value from flow1
}.launchIn(viewModelScope)

sharedFlow
.map { value -> value.id}
.distcintUntilChanged()
.flatMapLatest { id ->
    flow2(id)
}.onEach { value ->
    // handle value
}.launchIn(viewModelScope)

sharedFlow
.map { value -> value.id}
.distcintUntilChanged()
.flatMapLatest { id ->
    flow3(id)
}.onEach { value ->
    // handle value
}.launchIn(viewModelScope)

[Colton Idle]

oh boy. okay. lots of new apis there and kinda going over my head, but im going to try to learn some more of these starting tomorrow. thanks all