Android recyclerview item focus selection on dpad navigation

The main activity layout file with RecyclerView, activity_main.xml

The layout file for list item in the recyclerview, the focusable has to set to true, and the background is set to a selector drawable. list_item.xml

The background selector drawable, this will make the focused list item to display black background. item_selector.xml

MainActivity.kt

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.support.v7.widget.LinearLayoutManager
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

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

        val topics = listOf("Education","Finance","Government","Entertainment","Technology","Math","Biology","Physics","Chemistry","Space","Sports","Music","Animal","Countries","Weather","Politics","Traffic","Poverty","Social Media","Internet","Housing")
        val linearLayoutManager = LinearLayoutManager(this)
        val listAdapter = ItemListAdapter(topics)

        recycler_view.setHasFixedSize(true)
        recycler_view.layoutManager = linearLayoutManager
        recycler_view.adapter = listAdapter

    }
}

The adapter, ItemListAdapter.kt

import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import android.widget.Toast

class ItemListAdapter(private val itemList: List) : RecyclerView.Adapter() {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val layoutView = LayoutInflater.from(parent.context).inflate(R.layout.list_item, parent, false)
        return ViewHolder(layoutView)
    }

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

    override fun getItemCount() = itemList.size

    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView), View.OnClickListener {
        var tvTopic: TextView

        init {
            itemView.setOnClickListener(this)
            tvTopic = itemView.findViewById(R.id.topic) as TextView
        }
        override fun onClick(view: View) {
            Toast.makeText(view.context, "Clicked Position = " + adapterPosition, Toast.LENGTH_SHORT).show()
        }
    }
}

Complete example in Github