Kotlin - Cannot access method in another class

You need to call getEventId(position) on an instance of the class not on the class itself.

class MainActivity : AppCompatActivity(), RecyclerItemClickListener.OnRecyclerClickListener { private val eventsDatabase: DatabaseHelper = DatabaseHelper(this) private var events = ArrayList<Array<String>>() private var adapter = DataAdapter(arrayListOf<Array<String>>()) ... override fun onItemClick(view: View, position: Int) { var itemId = adapter.getEventId(position) Toast.makeText(this, "Normal tap on id: $itemId", Toast.LENGTH_SHORT).show() } ... } 

If you need to call getEventId(position) without instantiating your class (which I doubt might be the case here), you need to add it in your companion object.

class DataAdapter (events: ArrayList<Array<String>>) : RecyclerView.Adapter<DataAdapter.ViewHolder>() { private val TAG = "Adapter" private val events = events inner class ViewHolder (view: View) : RecyclerView.ViewHolder(view) { var id = "" val title: TextView = view.txtTitle val date: TextView = view.txtDate } companion object{ fun getEventId (position: Int): Int? { return if (events.isNotEmpty()) events[position][0].toInt() else null } } ..... }