Observe a MutableLiveData list

Question

I am using Live Data in my application and I have a view model that extends from ViewModel.

In my view model, I have a list that is:

var songs: MutableLiveData<List<Song>> = MutableLiveData<List<Song>>()

In a function in my view model I do this:

 songs.value?.find { it.id == song.id }.also {

                when (song.isFavorite) {
                    true -> song.isFavorite = false
                    false -> song.isFavorite = true
                }
            }

I will change a boolean in an item in songs and in m fragment I observe this list like below:

viewModel.songs.observe(this , Observer {

            Log.d(TAG , "songs changed")

        })

But songs will not notify after this change.

Why does this happen?

Thankyou for your answers.

Answer 1

How live data works is, when the value of the livedata changes then it will be notified for eg:

Let your data class of song:

data class Song(name : String?)

In ViewModel:

val songLiveData = MutableLiveData<Song?>

In your activity:

viewModel.songLiveData.observe(this , Observer {

        Log.d(TAG , "songs changed")

    })
songLiveData.value = Song(name = "Name of Song")

This will work.

When you call setValue of the live data than the callback comes to the observer.

private val songsLiveData = MutableLiveData<List<Song?>>()

init {
   songsLiveData.value = ArrayList()
}

fun editSong() {
    //change all the things in you live data
    songsLiveData.value = songsLiveData.value//this will give the callback to you observer
}