random uk lotto number generator

MainActivity.kt

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.widget.RadioButton
import kotlinx.android.synthetic.main.activity_main.*
import java.util.*

/*  
random UK lottery number generator. 
generates a specified quantity of random numbers
in the range of 1 to 59 (inclusive).
quantity of random numbers is selected by the user 
using radio buttons inside a radio group  
*/

class MainActivity : AppCompatActivity() {

    var qty = 6
    val max = 59
    val list = mutableListOf<Int>()
    lateinit var str: String

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

        supportActionBar?.hide()

        r5.isChecked = true
        radio_group.setOnCheckedChangeListener({ group, radio_id ->
            val radio: RadioButton = findViewById(radio_id)
            qty = Integer.parseInt(radio.text.toString())
        })

        button.setOnClickListener { gen() }
    }

    fun gen(){
        list.clear()
        str = ""
        button.isEnabled = false
        while (list.size < qty) {
            val n = Random().nextInt(max) + 1
            if (!list.contains(n)) list.add(n)
        }
        list.sort()

        for (i in 0 until list.size)
            str += "${list[i]} "

        text_view.text = str
        button.isEnabled = true
    }
}