【Kotlin/Android Studio】ItemTouchHelperの使い方！RecyclerViewでスワイプ処理を実装する方法

定義
abstract class ItemTouchHelper.SimpleCallback : ItemTouchHelper.Callback

class SwipeToCallback(private val adapter: MyListAdapter) : ItemTouchHelper.SimpleCallback(
    ItemTouchHelper.ACTION_STATE_IDLE,            // ドラッグの方向を指定
    ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT // スワイプの方向を指定
) {
  // 〜〜〜〜〜〜〜〜〜〜〜〜〜〜
}

ItemTouchHelper.SimpleCallback(
    ItemTouchHelper.ACTION_STATE_IDLE,            // サポートしない
    ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT // 左と右のスワイプをサポート
)

class SwipeToCallback(private val adapter: MyListAdapter) : ItemTouchHelper.SimpleCallback(
    ItemTouchHelper.ACTION_STATE_IDLE,            // ドラッグの方向を指定
    ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT // スワイプの方向を指定
) {
    override fun onMove(
        recyclerView: RecyclerView,
        viewHolder: RecyclerView.ViewHolder,
        target: RecyclerView.ViewHolder
    ): Boolean {
        // ドラッグアンドドロップの処理を実装
        return false
    }

    override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
        // スワイプしたアイテムを削除する処理を実装
        val position = viewHolder.adapterPosition
        adapter.deleteItem(position)
    }
}

Adapterクラス
fun deleteItem(position: Int) {
    if (position < 0 || position >= _userList.size) {
        return
    }
    _userList.removeAt(position)
    notifyItemRemoved(position)
}

val recyclerView: RecyclerView = view.findViewById(R.id.recyclerView)
recyclerView.layoutManager = LinearLayoutManager(view.context)
recyclerView.addItemDecoration(
    DividerItemDecoration(view.context, DividerItemDecoration.VERTICAL)
)
val adapter = MyListAdapter(data)
val swipeToCallback = SwipeToCallback(adapter)
val itemTouchHelper = ItemTouchHelper(swipeToCallback)
itemTouchHelper.attachToRecyclerView(recyclerView)
recyclerView.adapter = adapter

SwipeToCallback.kt
// スワイプ時の背景色とアイコンを描画
override fun onChildDraw(
    canvas: Canvas,
    recyclerView: RecyclerView,
    viewHolder: RecyclerView.ViewHolder,
    dX: Float,
    dY: Float,
    actionState: Int,
    isCurrentlyActive: Boolean
) {
    super.onChildDraw(canvas, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive)

    // 背景色を定義
    val background: ColorDrawable = ColorDrawable(Color.RED)

    // スワイプ時のアイコンを定義AppCompatResources
    val deleteIcon: Drawable? = AppCompatResources.getDrawable(recyclerView.context,R.drawable.delete)

    if (deleteIcon != null) {

      // 余白調整
      val itemView = viewHolder.itemView
      val iconMargin = (itemView.height - deleteIcon.intrinsicHeight) / 2
      val iconTop = itemView.top + (itemView.height - deleteIcon.intrinsicHeight) / 2
      val iconBottom = iconTop + deleteIcon.intrinsicHeight

      when {
          dX > 0 -> { // 右方向へのスワイプ
              val iconLeft = itemView.left + iconMargin
              val iconRight = itemView.left + iconMargin + deleteIcon.intrinsicWidth
              deleteIcon.setBounds(iconLeft, iconTop, iconRight, iconBottom)
              background.setBounds(itemView.left, itemView.top, itemView.left + dX.toInt(), itemView.bottom)
          }
          dX < 0 -> { // 左方向へのスワイプ
              val iconLeft = itemView.right - iconMargin - deleteIcon.intrinsicWidth
              val iconRight = itemView.right - iconMargin
              deleteIcon.setBounds(iconLeft, iconTop, iconRight, iconBottom)
              background.setBounds(itemView.right + dX.toInt(), itemView.top, itemView.right, itemView.bottom)
          }
          else -> {
              background.setBounds(0, 0, 0, 0)
          }
      }
      // 背景の描画
      background.draw(canvas)
      // アイコンの描画
      deleteIcon.draw(canvas)
    }
}

dX > 0 -> { // 右方向へのスワイプ
    background.setBounds(itemView.left, itemView.top, itemView.left + dX.toInt(), itemView.bottom)
    background.draw(canvas)

    val text = "右スワイプ"
    val paint = Paint()
    paint.color = Color.WHITE
    paint.textSize = 40f
    val textLeft = itemView.left + iconMargin
    val centerY = itemView.top + itemView.height / 2
    val textHeight = (paint.descent() + paint.ascent()) / 2
    val textY = centerY - textHeight
    canvas.drawText(text, textLeft.toFloat(), textY, paint)
}

override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
    if (direction == ItemTouchHelper.LEFT) {
        // 左スワイプ時に実行したい処理
    } else if (direction == ItemTouchHelper.RIGHT) {
        // 右スワイプ時に実行したい処理
    }
}

override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
    AlertDialog.Builder(context)
        .setTitle("削除しますか？")
        .setPositiveButton("OK", { dialog, which ->
            /// スワイプしたアイテムを削除する処理を実装
            val position = viewHolder.adapterPosition
            adapter.deleteItem(position)
        })
        .setNegativeButton("キャンセル", { dialog, which ->
            // キャンセルされた場合はRecyclerViewを更新
            val position = viewHolder.adapterPosition
            adapter.updateItem(position)
        })
        .show()
}

ListAdapter.kt
public fun updateItem(position: Int) {
    if (position < 0 || position >= _borrowerList.size) {
        return
    }
    val item = _borrowerList[position]
    viewModel.updateBorrower(item.id,item.name)
    notifyItemChanged(position)
}