MainActivity.kt

class MainActivity : AppCompatActivity() {

    private lateinit var scrollView: ScrollView
    private lateinit var dragLinearLayout: DragLinearLayout

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

        scrollView = findViewById(R.id.scroll_view)
        dragLinearLayout = findViewById<DragLinearLayout>(R.id.drag_linear_layout).apply {
            setContainerScrollView(scrollView)
            setOnViewSwapListener { _, startPosition, _, endPosition ->
                swapElements(startPosition, endPosition)
            }
        }
        ...
    }
    ...
    private fun swapElements(startPosition: Int, endPosition: Int) {
        addedCurrencies.run {
            this[startPosition] = this[endPosition].also {
                this[endPosition] = this[startPosition]
            }
        }
    }
  ...
}