ListAdapter not updating item in reyclerview

问题:

I'm using the new support library ListAdapter. Here's my code for the adapter

class ArtistsAdapter : ListAdapter<Artist, ArtistsAdapter.ViewHolder>(ArtistsDiff()) {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        return ViewHolder(parent.inflate(R.layout.item_artist))
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.bind(getItem(position))
    }

    class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        fun bind(artist: Artist) {
            itemView.artistDetails.text = artist.artistAlbums
                    .plus(" Albums")
                    .plus(" \u2022 ")
                    .plus(artist.artistTracks)
                    .plus(" Tracks")
            itemView.artistName.text = artist.artistCover
            itemView.artistCoverImage.loadURL(artist.artistCover)
        }
    }
}

I'm updating the adapter with

musicViewModel.getAllArtists().observe(this, Observer {
            it?.let {
                artistAdapter.submitList(it)
            }
        })

My diff class

class ArtistsDiff : DiffUtil.ItemCallback<Artist>() {
    override fun areItemsTheSame(oldItem: Artist?, newItem: Artist?): Boolean {
        return oldItem?.artistId == newItem?.artistId
    }

    override fun areContentsTheSame(oldItem: Artist?, newItem: Artist?): Boolean {
        return oldItem == newItem
    }
}

What's happening is when submitList is called the first time the adapter renders all the items, but when submitList is called again with updated object properties it does not re-render the view which has changed.

It re-renders the view as I scroll the list, which in turn calls bindView()

Also, I've noticed that calling adapter.notifyDatasSetChanged() after submit list renders the view with updated values, but I don't want to call notifyDataSetChanged() because the list adapter has diff utils built-in

Can anyone help me here?

回答1:

Edit: I understand why this happens that wasn't my point. My point is that it at least needs to give a warning or call the notifyDataSetChanged() function. Because apparently I am calling the submitList(...) function for a reason. I am pretty sure people are trying to figure out what went wrong for hours until they figure out the submitList() ignores silently the call.

This is because of Googles weird logic. So if you pass the same list to the adapter it does not even call the DiffUtil.

public void submitList(final List<T> newList) {
    if (newList == mList) {
        // nothing to do
        return;
    }
....
}

I really don't understand the whole point of this ListAdapter if it can't handle changes on the same list. If you want to change the items on the list you pass to the ListAdapter and see the changes then either you need to create a deep copy of the list or you need to use regular RecyclerView with your own DiffUtill class.

回答2:

The library assumes you are using Room or any other ORM which offers a new async list every time it gets updated, so just calling submitList on it will work, and for sloppy developers, it prevents doing the calculations twice if the same list is called.

The accepted answer is correct, it offers the explanation but not the solution.

What you can do in case you're not using any such libraries is:

submitList(null);
submitList(myList);

Another solution would be to override submitList (which doesn't cause that quick blink) as such:

@Override
public void submitList(final List<Author> list) {
    super.submitList(list != null ? new ArrayList<>(list) : null);
}

Kinda retarded logic but works perfectly. My preferred method is the second one because it doesn't cause each row to get an onBind call.

回答3:

According to the official docs :

Whenever you call submitList it submits a new list to be diffed and displayed.

This is why whenever you call submitList on the previous (already submitted list), it does not calculate the Diff and does not notify the adapter for change in the dataset.