I have a simple

Flow

wrapper around

LiveData

and I have a problem, because it closes (

invokeOnClose

is called) immediately after first value is emitted by

Observer

.

fun <T> LiveData<T>.asFlow(): Flow<T> = channelFlow {
    value?.let { offer(it) }
    val observer = Observer<T> { t -> t?.let(this::offer) }
    observeForever(observer)
    invokeOnClose {
        removeObserver(observer)
    }
}

To be sure my

CoroutineScope

is not causing this cancellation, I run this also in

GlobalScope

and the behaviour was the same. How can I see what is causing cancellation? I analysed stack trace, but I didn’t see anything interesting there.

Try it https://github.com/icerockdev/moko-mvvm/blob/22b50b8919c565d2de24738c9183c93cc475fdc7/mvvm/src/commonMain/kotlin/dev/icerock/moko/mvvm/livedata/LiveDataCoroutines.kt#L13

Thank you. In a code you posted there is a custom

LiveData

implementation, it have

addObserver

function which is not available in Android’s LiveData even though it can be replaced with

observeForever

. What is interesting, I looked at this code again and decided to give a try to

awaitClose

function and it seems to work as expected - Channel is not closed immediately. When I’m using

invokeOnClose

, then Channel is closed. Can anyone explain why it acts like that? To conclude, when I changed function body to this one:

fun <T> LiveData<T>.asFlow(): Flow<T> = channelFlow {
    value?.let { offer(it) }
    val observer = Observer<T> { t -> t?.let(this::offer) }
    observeForever(observer)
    awaitClose {
        removeObserver(observer)
    }
}

I get expected behavior, so channel is not closed immediately and it’s offering events from LiveData.

The channel is closed, once the scope exists.

awaitClose

waits for the channel to be closed before returning.

Thank you for the reply, but I still don’t understand that. Why when I’m calling

invokeOnClose

it’s effectively closes the Channel (and executes lambda) while

awaitClose

not? I thought both of them should just be called when “something” called

close

on the Channel

invokeOnClose

does what it says and what you expect. It's just that after you call

invokeOnClose

, the code in the

channelFlow

lambda is done and once that happens

channelFlow

closes the channel, which then calls

invokeOnClose

.....

awaitOnClose

happens to also suspend the

channelFlow

lambda until the channel is closed in some other way.

Thank you 🙂