codingsystems

 import androidx.appcompat.app.AppCompatActivity

import android.os.Bundle
import android.widget.Button
import android.widget.ImageView
import android.widget.TextView
import kotlin.random.Random


class MainActivity : AppCompatActivity() {

    lateinit var diceImage: ImageView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val rollButton: Button = findViewById(R.id.Roll_Button)
        rollButton.text = "Let's Roll"
        rollButton.setOnClickListener{
            rollDice()
        }

        diceImage = findViewById(R.id.dice_Image)
    }

    private fun rollDice() {
        val dice = Dice(6)
        val diceroll = dice.roll()

        // val randomInt = Random().nextInt(6) + 1
        val drawableResource = when (rollDice) {
            1 -> R.drawable.dice_1
            2 -> R.drawable.dice_2
            3 -> R.drawable.dice_3
            4 -> R.drawable.dice_4
            5 -> R.drawable.dice_5
            else -> R.drawable.dice_6
        }

        diceImage.setImageResource(drawableResource)
    }
}

class Dice(val numSides: Int) {
    fun roll(): Int {
        return(1..numSides).random()
    }
}

My code 

compare to

Udacity code

package com.example.android.diceroller

import android.os.Bundle
import android.widget.Button
import android.widget.ImageView
import androidx.appcompat.app.AppCompatActivity
import java.util.*

class MainActivity : AppCompatActivity() {

    lateinit var diceImage: ImageView

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

        val rollButton: Button = findViewById(R.id.roll_button)
        rollButton.setOnClickListener {
            rollDice()
        }

        diceImage = findViewById(R.id.dice_image)
    }

    private fun rollDice() {
        val randomInt = Random().nextInt(6) + 1
        val drawableResource = when (randomInt) {
            1 -> R.drawable.dice_1
            2 -> R.drawable.dice_2
            3 -> R.drawable.dice_3
            4 -> R.drawable.dice_4
            5 -> R.drawable.dice_5
            else -> R.drawable.dice_6
        }

        diceImage.setImageResource(drawableResource)
    }
}