Alert Dialog with SingleItemSelection in Android

package org.geeksforgeeks.demo

import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import androidx.appcompat.app.AlertDialog
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {

    private lateinit var bOpenAlertDialog: Button
    private lateinit var tvSelectedItemPreview: TextView

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

        bOpenAlertDialog = findViewById(R.id.openAlertDialogButton)
        tvSelectedItemPreview = findViewById(R.id.selectedItemPreview)

        // single item array instance to store which element
        // is selected by user initially it should be set to
        // zero meaning none of the element is selected by default
        val checkedItem = intArrayOf(-1)

        bOpenAlertDialog.setOnClickListener {
        
            // AlertDialog builder instance to build the alert dialog
            val alertDialog = AlertDialog.Builder(this)
                // set the custom icon to the alert dialog
                .setIcon(R.mipmap.ic_launcher_round)
                // title of the alert dialog
                .setTitle("Choose an Item")

            val listItems = arrayOf("Android Development", "Web Development", "Machine Learning")

            // the function setSingleChoiceItems is the function which
            // builds the alert dialog with the single item selection
            alertDialog.setSingleChoiceItems(listItems, checkedItem[0]) { dialog, which ->
                
                // update the selected item which is selected by the
                // user so that it should be selected when user opens
                // the dialog next time and pass the instance to setSingleChoiceItems method
                checkedItem[0] = which

                // now also update the TextView which previews the selected item
                tvSelectedItemPreview.text = buildString {
                    append("Selected Item is :\n")
                    append(listItems[which])
                }

                // when selected an item the dialog should be closed
                // with the dismiss method
                dialog.dismiss()
            }

            // create and build the AlertDialog instance with the
            // AlertDialog builder instance
            val customAlertDialog = alertDialog.create()

            // show the alert dialog when the button is clicked
            customAlertDialog.show()
        }
    }
}