I ve got a couple of `StateFlows` the second depends on the kotlinlang #coroutines

private val playlist = playlistRepository.getPlaylists(PlaylistQuery.PlaylistId(initialPlaylist.id))
        .map { playlists ->
            playlists.firstOrNull()
        }
        .filterNotNull()
        .stateIn(
            scope = this,
            started = SharingStarted.WhileSubscribed(),
            initialValue = initialPlaylist
        )

    private val playlistSongs: StateFlow<List<PlaylistSong>> = playlist
        .flatMapConcat { playlist ->
            playlistRepository.getSongsForPlaylist(playlist.id, playlist.sortOrder)
        }
        .stateIn(
            scope = this,
            started = SharingStarted.WhileSubscribed(),
            initialValue = emptyList()
        )

playlistSongs

depends on

playlists

. When

playlist

is re-emitted, I expect

playlistSongs

to flatmap the new

playlist

, and potentially emit a new set of playlistSongs But the

flatMapConcat

block in

playlistSongs

doesn't seem to get called, even after

playlist

emits. Both flows are collected in

bindView()

(called in

Fragment.onViewCreated()

Copy code

override fun bindView(view: PlaylistDetailContract.View) {
    super.bindView(view)

    launch {
        playlist.collect { playlist ->
            foo()
        }
    }
    launch {
        playlistSongs.collect { playlistSongs ->
            bar()
        }
    }
}

mateusz.kwiecinski

06/08/2021, 4:47 AM

When
playlist
is re-emitted

re-emitted

you mean exactly the same value gets emitted?

Tim Malseed

06/08/2021, 4:47 AM

No. The

playlist

object is a new instance and not equal.

playlistRepository.getSongsForPlaylist()

is not called even though

playlist

emits a new, not-equal

playlist

mateusz.kwiecinski

06/08/2021, 4:49 AM

and does

getSongsForPlaylist

get called for the first time? When first

playlits

value is emitted?

Tim Malseed

06/08/2021, 4:49 AM

Yes

mateusz.kwiecinski

06/08/2021, 4:50 AM

ok then, my guess would be the

getSongsForPlaylist

called for the first

playlist

emitted never completes

Tim Malseed

06/08/2021, 4:51 AM

OK. You're probably right! I need to think this over

mateusz.kwiecinski

06/08/2021, 4:51 AM

you probably would like to cancel collecting

getSongsForPlaylist

if a new playlist is emitted

Tim Malseed

06/08/2021, 4:53 AM

Do you have any suggestions as to how/where to cancel that?

mateusz.kwiecinski

06/08/2021, 4:54 AM

Use

flatMapLatest

instead of

flatMapConcat

💯 1

Tim Malseed

06/08/2021, 4:55 AM

Thanks so much! Been trying to figure this one out for a while!

👍 1

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