How to unsubscribe from live data in RecyclerView adapters?

[mpivchev]

I am trying to update a progress bar on the first item of a RecyclerView using live data, however it doesn't seem to unsubscribe properly so other items also get included into it. Any way to make it unsubscribe properly?

   if (position == 0) {
            ExoPlayerManager.currentPlaytime.addObserver {
                b.progress.max = ExoPlayerManager.exoPlayer.duration.toInt()
                b.progress.progress = it.toInt()
            }
        } else {
            ExoPlayerManager.currentPlaytime.removeObserver { }
            b.icon.setImageDrawable(ContextCompat.getDrawable(b.root.context, R.drawable.ic_music_note))
            b.root.alpha = 0.5f
            b.progress.progress = 0
            b.progress.max = 0
        }

The live data resides here:

object ExoPlayerManager {
    lateinit var exoPlayer: SimpleExoPlayer
    private lateinit var context: Context
    private val handler = Handler()
    val currentPlaytime: MutableLiveData<Long> = MutableLiveData(initialValue = 0)
    //....

The first item updates properly:

... but so does the last item:

[Alex009]

hi! you are using lambda incorrectly:

ExoPlayerManager.currentPlaytime.addObserver {
    ...
}

is equal:

val firstLambda = {
    ...
}
ExoPlayerManager.currentPlaytime.addObserver(firstLambda)

and:

ExoPlayerManager.currentPlaytime.removeObserver { }

equal to:

val secondLambda = { }
ExoPlayerManager.currentPlaytime.removeObserver(secondLambda)

i.e. you remove another observer, not those what was added before. so to fix code you should save lamda in class property and add/remove it in correct time:

val progressObserver = {
                b.progress.max = ExoPlayerManager.exoPlayer.duration.toInt()
                b.progress.progress = it.toInt()
            }

...

if (position == 0) {
            ExoPlayerManager.currentPlaytime.addObserver(progressObserver)
        } else {
            ExoPlayerManager.currentPlaytime.removeObserver(progressObserver)
            b.icon.setImageDrawable(ContextCompat.getDrawable(b.root.context, R.drawable.ic_music_note))
            b.root.alpha = 0.5f
            b.progress.progress = 0
            b.progress.max = 0
        }

[mpivchev]

Hi Alex, sadly with those changes the problem still occurs.

This is how it looks like now:

 val progressObserver : (progress: Long) -> Unit = {
            b.progress.max = ExoPlayerManager.exoPlayer.duration.toInt()
            b.progress.progress = it.toInt()
        }

        if (position == 0) {
            ExoPlayerManager.currentPlaytime.addObserver (progressObserver)
        } else {
            ExoPlayerManager.currentPlaytime.removeObserver(progressObserver)
            b.icon.setImageDrawable(ContextCompat.getDrawable(b.root.context, R.drawable.ic_music_note))
            b.root.alpha = 0.5f
            b.progress.progress = 0
            b.progress.max = 0
        }

[Alex009]

you store progressObserver as ViewHolder property or it just local variable? it should be class property. if it local variable you got just same code what was on start.

class MyViewHolder {
    val progressObserver : (progress: Long) -> Unit = {
            b.progress.max = ExoPlayerManager.exoPlayer.duration.toInt()
            b.progress.progress = it.toInt()
        }

    fun bind(position: Int) {
        if (position == 0) {
            ExoPlayerManager.currentPlaytime.addObserver (progressObserver)
        } else {
            ExoPlayerManager.currentPlaytime.removeObserver(progressObserver)
            b.icon.setImageDrawable(ContextCompat.getDrawable(b.root.context, R.drawable.ic_music_note))
            b.root.alpha = 0.5f
            b.progress.progress = 0
            b.progress.max = 0
        }
    }
}

you should use in addObserver and removeObserver one object