MainActivity.kt

package com.example.quickmax

import android.os.Bundle
import android.view.View
import android.widget.RadioButton
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

    var numberSet = NumberSet(4, 3)

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

        addRadioButtons()
    }

    private fun addRadioButtons() {
        for (n in numberSet) {
            val radioButton = RadioButton(this)
            radioButton.id = View.generateViewId()
            radioButton.text = n.toString()
            radioButton.setOnClickListener { processAnswer(n) }
            radio_group.addView(radioButton)
        }
    }

    private fun processAnswer(answer: Int) {
        if (numberSet.isCorrect(answer)) {

            response.text = getString(R.string.response_correct)
        }
        else
            response.text = getString(R.string.response_wrong)
    }
}