AdapterUpdatable for Kotlin (RecyclerView+DiffUtil)

AdapterUpdatable.kt

interface AdapterUpdatable<TYPE> {
  companion object {
    private const val DEFAULT_UPDATE_CURRENT_LIST = false
  }

  val list: MutableList<TYPE>

  fun update(
    newList: List<TYPE>,
    updateCurrentList: Boolean = DEFAULT_UPDATE_CURRENT_LIST,
    comparatorToUpdateCurrentList: (TYPE, TYPE) -> Boolean = { x, y -> x == y }
  ) {
    update(this as RecyclerView.Adapter<*>, list, newList, updateCurrentList, comparatorToUpdateCurrentList)
  }

  private fun update(
    adapter: RecyclerView.Adapter<*>,
    oldList: MutableList<TYPE>,
    newList: List<TYPE>,
    updateCurrentList: Boolean,
    comparatorToUpdateCurrentList: (TYPE, TYPE) -> Boolean
  ) {
    if (updateCurrentList) {
      adapter.update(oldList, newList, comparatorToUpdateCurrentList)
    } else {
      update(newList)
    }

    adapter.notifyDataSetChanged()
  }

  private fun RecyclerView.Adapter<*>.update(
    oldList: List<TYPE>,
    newList: List<TYPE>,
    comparator: (TYPE, TYPE) -> Boolean
  ) {
    val diff = DiffUtil.calculateDiff(object : DiffUtil.Callback() {
      override fun areItemsTheSame(
        oldItemPosition: Int,
        newItemPosition: Int
      ): Boolean = comparator(oldList[oldItemPosition], newList[newItemPosition])

      override fun areContentsTheSame(
        oldItemPosition: Int,
        newItemPosition: Int
      ): Boolean = oldList[oldItemPosition] == newList[newItemPosition]

      override fun getOldListSize() = oldList.size

      override fun getNewListSize() = newList.size
    })

    update(newList)
    diff.dispatchUpdatesTo(this)
  }

  private fun update(newList: List<TYPE>) {
    list.run {
      clear()
      addAll(newList)
    }
  }
}