Collecting flow 2 times from Room database

Question

I have problem with collection songs from my database.

Song Dao:

   @Query("SELECT * FROM song_table")
    fun observeSongs() : Flow<List<DatabaseSongListItem>>

Repository:

fun observeSongs() = songDao.observeSongs()

ViewModel:

 private val _observeSongs = MutableStateFlow(emptyList<DatabaseSongListItem>())
    val observeSongs = _observeSongs.asStateFlow()
    viewModelScope.launch {
            songListRepository.getSongs() -> this line can get api songs + it add songs to database
            songListRepository.observeSongs().collect(){ songs ->
                _observeSongs.value = songs
            }
        }

MainActivity:

  lifecycleScope.launch {
            viewModel.observeSongs.collect {
                Log.d(ContentValues.TAG, "MAIN: $it")
            }

This code is working but im collecting my songs 2 times, 1 in viewModel and another one i activiy. I only want to collect it in my activity once. But when I use this line of code in viewModel I get this:

 _observeSongs.value = songListRepository.observeSongs()
Type mismatch.
Required:
List<DatabaseSongListItem>
Found:
Flow<List<DatabaseSongListItem>>

I want to show list of songs in recyclerView that is why I need List of songs.

Answer 1

I'm still unclear on exactly what your issue is. The clean way I would create a state flow and observe it is as follows, but I don't know if this achieves what you're trying to do exactly.

The SharingStarted setting will prevent unnecessary monitoring of the database when the Activity is off-screen, but it's optional.

ViewModel:

val observeSongs = songListRepository.observeSongs()
    .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), emptyList())

init { // I'm assuming you were doing this in init, but maybe you have it in a function
    viewModelScope.launch { songListRepository.getSongs() }
}

Activity:

lifecycleScope.launch {
    viewModel.observeSongs.collect {
        myRecyclerViewAdapter.submitList(it)
    }
}

// or alternate syntax:
viewModel.observeSongs
    .onEach { myRecyclerViewAdapter.submitList(it) }
    .launchIn(lifecycleScope)