SampleAdapter.kt

class SampleAdapter : RecyclerView.Adapter<SampleViewHolder>() {

    private var itemList: List<SampleItem> = listOf()

    fun setItems(newList: List<SampleItem>) {
        val diffItemCallback = object : DiffUtil.Callback() {

            override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int) =
                this.itemList[oldItemPosition].getItemId() == newList[newItemPosition].getItemId()

            override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int) =
                this.itemList[oldItemPosition].getDiff() == newList[newItemPosition].getDiff()

            override fun getOldListSize() = itemList.size

            override fun getNewListSize() = newList.size
        }

        val diffResult = DiffUtil.calculateDiff(diffItemCallback)
        diffResult.dispatchUpdatesTo(this@SampleAdapter)
    }
  
  (...)
}