Android RecylerView ListAdapter (Kotlin)

class AlbumListFragment : Fragment() {    private val viewModel by viewModels<AlbumListViewModel>()    private lateinit var adapter: LocalAdapter    override fun onCreateView(        inflater: LayoutInflater, container: ViewGroup?,        savedInstanceState: Bundle?    ): View? {        return inflater.inflate(R.layout.albumlist, container, false)    }    override fun onActivityCreated(savedInstanceState: Bundle?) {        super.onActivityCreated(savedInstanceState)        initList()    }    private fun initList() {        adapter = LocalAdapter(viewModel)        list.adapter = adapter        val items = mutableListOf<ViewItem>()        // TODO: load items        adapter.submitList(items)    }    sealed class ViewItem(open val id: String, val resource: Int) {        data class AlbumItem(override val id: String, val title: String, val childCount: Int) : ViewItem(id, R.layout.albumlist_item)    }    class LocalAdapter(val viewModel: AlbumListViewModel) : ListAdapter<ViewItem, LocalAdapter.ViewHolder>(DiffCallback()) {        override fun getItemViewType(position: Int): Int {            return getItem(position).resource        }        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {            val view = LayoutInflater.from(parent.context)                .inflate(viewType, parent, false)            return ViewHolder(view)        }        override fun onBindViewHolder(holder: ViewHolder, position: Int) {            holder.bind(getItem(position))        }        private class DiffCallback: DiffUtil.ItemCallback<ViewItem>() {            override fun areItemsTheSame(oldItem: ViewItem, newItem: ViewItem): Boolean {                if (oldItem.resource != newItem.resource) return false                // check if id is the same                return oldItem.id == newItem.id            }            @SuppressLint("DiffUtilEquals")            override fun areContentsTheSame(oldItem: ViewItem, newItem: ViewItem): Boolean {                // check if content is the same                // equals using data class                return oldItem == newItem            }        }        inner class ViewHolder(override val containerView: View) : RecyclerView.ViewHolder(containerView),            LayoutContainer {            // why update ui here? easier to access view without need to holder.titleTextView            fun bind(item: ViewItem) {                when(item) {                    is ViewItem.AlbumItem -> {                        titleTextView.text = item.title                        detailTextView.text = "${item.childCount} items"                    }                }            }        }    }}

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context=".view.AlbumListFragment">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/list"
        app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</FrameLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:fresco="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="@dimen/margin16"
    >

    <TextView
        android:id="@+id/titleTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="@dimen/margin8"
        android:layout_marginBottom="@dimen/margin8"
        tools:text="Title" />

    <TextView
        android:id="@+id/detailTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textAppearance="@style/TextAppearance.AppCompat.Small"
        tools:text="10 items" />
</LinearLayout>