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.

Solution

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
}