RecycleView selection library - holding an item fires onSelectionChanged several times - android-recyclerview

Question

I implemented a simple RecyclerView example, with multiple items selection possibility, using the selection library.
Here's my code:
class MainActivity : AppCompatActivity() {
private var listOfItems = ArrayList<Item>()
private var selectionTracker: SelectionTracker<Long>? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val recyclerView = findViewById<RecyclerView>(R.id.rvMainRecyclerView)
for (i in 0..32) {
listOfItems.add(Item(i, "Item $i"))
}
val recyclerViewAdapter = RecyclerViewAdapter(listOfItems)
recyclerView.adapter = recyclerViewAdapter
selectionTracker = SelectionTracker.Builder<Long>(
"Itemselection",
recyclerView,
MyItemKeyProvider(recyclerView),
MyItemDetailsLookup(recyclerView),
StorageStrategy.createLongStorage()
).build()
selectionTracker?.addObserver(
object: SelectionTracker.SelectionObserver<Long>() {
override fun onSelectionChanged() {
super.onSelectionChanged()
val itemsSelected = selectionTracker?.selection?.size()
Log.d("MainActivity", "$itemsSelected items selected")
}
}
)
recyclerViewAdapter.tracker = selectionTracker
}
}
class RecyclerViewAdapter(
val dataSet: ArrayList\<Item\>
): RecyclerView.Adapter\<RecyclerViewAdapter.ViewHolder\>() {
var tracker: SelectionTracker<Long>? = null
init {
setHasStableIds(true)
}
inner class ViewHolder(view: View): RecyclerView.ViewHolder(view) {
val textView: TextView
init {
textView = view.findViewById(R.id.tvRecyclerViewItemTitle)
}
fun getItemDetails(): ItemDetails<Long> {
return object : ItemDetails<Long>() {
override fun getPosition(): Int {
return adapterPosition
}
override fun getSelectionKey(): Long? {
return itemId
}
}
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
return ViewHolder(LayoutInflater
.from(parent.context).inflate(R.layout.recycler_view_item, parent, false))
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val currentItem = dataSet[position]
holder.textView.text = currentItem.value
holder.itemView.isActivated = tracker!!.isSelected(position.toLong())
}
override fun getItemCount(): Int {
return dataSet.size
}
override fun getItemId(position: Int): Long {
return dataSet[position].id.toLong()
}
}
I'm curious why the onSelectionChanged (in MainActivity selectionTracker?.addObserver...) is triggered several times while I hold an item to start selection mode?
To be more precise, this is the use case:
Nothing is selected,
Long click on any item => selection mode activated; the item is selected
Here, "1 items selected" is being printed out as long as I hold the first item.