【Android】＜Kotlin＞ItemTouchHelperを使って、リストの項目をスワイプして削除する方法を徹底解説！

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

class MainActivity : AppCompatActivity() {

    private lateinit var recyclerView: RecyclerView
    private lateinit var adapter: ItemAdapter

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        recyclerView = findViewById(R.id.recyclerView)
        val items = mutableListOf("Item 1", "Item 2", "Item 3", "Item 4")

        adapter = ItemAdapter(items)
        recyclerView.layoutManager = LinearLayoutManager(this)
        recyclerView.adapter = adapter

        val itemTouchHelper = ItemTouchHelper(SwipeToDeleteCallback(adapter))
        itemTouchHelper.attachToRecyclerView(recyclerView)
    }
}

class SwipeToDeleteCallback(private val adapter: ItemAdapter) : ItemTouchHelper.Callback() {

    override fun getMovementFlags(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder): Int {
        val swipeFlags = ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT
        return makeMovementFlags(0, swipeFlags)
    }

    override fun onMove(
        recyclerView: RecyclerView,
        viewHolder: RecyclerView.ViewHolder,
        target: RecyclerView.ViewHolder
    ): Boolean {
        // ドラッグ操作は使用しないためfalseを返す
        return false
    }

    override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
        val position = viewHolder.adapterPosition
        adapter.removeItem(position)
    }
}

class ItemAdapter(private val items: MutableList<String>) : RecyclerView.Adapter<ItemAdapter.ViewHolder>() {

    class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val textView: TextView = itemView.findViewById(R.id.itemText)
    }

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

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.textView.text = items[position]
    }

    override fun getItemCount(): Int = items.size

    fun removeItem(position: Int) {
        items.removeAt(position)
        notifyItemRemoved(position)
    }
}

override fun onChildDraw(
    c: Canvas,
    recyclerView: RecyclerView,
    viewHolder: RecyclerView.ViewHolder,
    dX: Float,
    dY: Float,
    actionState: Int,
    isCurrentlyActive: Boolean
) {
    val itemView = viewHolder.itemView
    val paint = Paint().apply { color = Color.RED }
    c.drawRect(
        itemView.left.toFloat(),
        itemView.top.toFloat(),
        itemView.right + dX,
        itemView.bottom.toFloat(),
        paint
    )
    super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive)
}