dk_mvvm_2.kt

class MainViewModel(val view: MainView) {

    private var currentItem: Item by Delegates.observable(Item.ITEM_A,
        { _: KProperty<*>, oldItem: Item, newItem: Item ->
            view.onUpdatedItem(oldItem, newItem)
        })

    fun onClicked(item: Item) {
        currentItem = item
    }
}