I've got a couple of `StateFlows` the second depends on the first. But, the second is not emitting w...

# coroutines

[Tim Malseed]

I've got a couple of StateFlows the second depends on the first. But, the second is not emitting when I expect it to..

[Tim Malseed]

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()
        )

[Tim Malseed]

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() :

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

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

[mateusz.kwiecinski]

When playlist is re-emitted

by re-emitted you mean exactly the same value gets emitted?

[Tim Malseed]

No. The playlist object is a new instance and not equal.

[Tim Malseed]

playlistRepository.getSongsForPlaylist() is not called even though playlist emits a new, not-equal playlist.

[mateusz.kwiecinski]

and does getSongsForPlaylist get called for the first time? When first playlits value is emitted?

[Tim Malseed]

Yes

[mateusz.kwiecinski]

ok then, my guess would be the getSongsForPlaylist called for the first playlist emitted never completes

[Tim Malseed]

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

[mateusz.kwiecinski]

you probably would like to cancel collecting getSongsForPlaylist if a new playlist is emitted

[Tim Malseed]

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

[mateusz.kwiecinski]

Use flatMapLatest instead of flatMapConcat

[Tim Malseed]

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