Recycler view adapter

Adapter.kt

class GalleryAdapter(var items:List<DataHolder>) : Adapter<GalleryAdapter.ViewHolder>() {
    override fun onBindViewHolder(holder: ViewHolder,
                                  position: Int) {
        TODO("not implemented") // File | Settings | File Templates.
    }

    override fun getItemCount(): Int = items.size

    override fun onCreateViewHolder(parent: ViewGroup,
                                    viewType: Int): ViewHolder {
        val inflater = LayoutInflater.from(parent.context)
        val view = inflater.inflate(layout.w_icon_label_checkbox, parent, false)
        return ViewHolder(view)
    }

    class ViewHolder(v: View) : RecyclerView.ViewHolder(v) {
        var icon: ImageView? = v.v_icon
    }

    fun updateAppsList(list: List<DataHolder>) {
        Timber.v("jsp updating apps list. New size: ${list.size}")

        val diffRes = DiffUtil.calculateDiff(DiffDataCallback(items, list))
        items = list
        diffRes.dispatchUpdatesTo(this)
    }
}

DataHolder.kt

class DataHolder(var data:String)

DiffCallback.kt

class DiffDataCallback(var itemsOld: List<DataHolder>,
                       var itemsNew: List<DataHolder>
                      ) : Callback() {

    override fun areItemsTheSame(oldItemPosition: Int,
                                 newItemPosition: Int): Boolean {
        val itemOld = itemsOld[oldItemPosition]
        val itemNew = itemsNew[newItemPosition]
        return itemNew.data == itemOld.data
    }

    override fun areContentsTheSame(oldItemPosition: Int,
                                    newItemPosition: Int): Boolean {
        return true
    }


    override fun getOldListSize(): Int = itemsOld.size

    override fun getNewListSize(): Int = itemsNew.size
}