When I collect a flow I run into the problem that ...

# flow

[Tobias]

When I collect a flow I run into the problem that although the value gets changed nothing happens

val monitorDongleEuiJob = settings.dongleEui.takeWhile { dongleEui ->
        dongleEui.isNotEmpty()
    }.onEach { dongleEui ->
        // do something, but nothing happens
    }.catch {
        print(it.message)
    }.launchIn(coroutineScope)

When I change the code to this, it always works, but I don’t undestand why

val monitorDongleEuiJob = settings.dongleEui.onEach { dongleEui ->
    if (dongleEui.isEmpty()) {
        return@onEach
    }
    // do something
}.catch {
    print(it.message)
}.launchIn(coroutineScope)

Shouldn’t it basically be the same?

Or am I misunderstanding takeWhile? Maybe does it stop collection when the condition has been met?

[Sam]

The two code examples aren't equivalent. return@onEach won't terminate the flow, it's just a no-op.

[Tobias]

@Sam So takeWhile terminates it? Then I have found my misunderstanding.

[Sam]

Yes, takeWhile is designed to end the flow once its value changes from true to false. Maybe you're looking for filter instead?

[Tobias]

Ah, now I got it. Thanks a log @Sam

Changed it to

val monitorDongleEuiJob = settings.dongleEui
    .filter { it.isNotEmpty() }
    .onEach { dongleEui ->
...

I think this is what I actually need.

[Tobias]

Many thanks @Sam!