Вы не можете запросить ViewModel перед ошибкой вызова onCreate

Question

Работаю над тем, чтобы заставить мое приложение работать, когда я поворачиваю экран. Я поместил свои вопросы и ответы в модель представления под названием QuizViewModel. Когда я пытаюсь запустить свое приложение, я получаю сообщение, что не могу запросить ViewModel до вызова onCreate и ошибки NullPointerException.

Я попытался вызвать вызов моей viewModel после onCreate и получить те же результаты. Я не знаю, что я мог сделать неправильно. Как я могу исправить эту проблему?

import android.content.res.ColorStateList
import android.graphics.Color
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.ViewModelProvider

class QuizActivity : AppCompatActivity() {    

    private val defaultButtonColor = "#00a2ff"
    private val selectedButtonColor = "#cb297b"

    // view fields
    private lateinit var questionTextView: TextView
    private lateinit var answerButtonList: List<Button>
    private lateinit var hintButton: Button
    private lateinit var submitButton: Button

    private val quizViewModel: QuizViewModel by lazy {
        ViewModelProvider(this).get(QuizViewModel::class.java)
    }

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


        // initialize views
        questionTextView = findViewById(R.id.question_text_view)
        answerButtonList = listOf(
            findViewById(R.id.answer_0_button),
            findViewById(R.id.answer_1_button),
            findViewById(R.id.answer_2_button),
            findViewById(R.id.answer_3_button)
        )
        hintButton = findViewById(R.id.hint_button)
        submitButton = findViewById(R.id.submit_button)   


        // attach listeners to answer buttons
        for(index in answerButtonList.indices){
            answerButtonList[index].setOnClickListener {
                processAnswerButtonClick(index)
            }
        }

        // attach listeners to hint button and submit button
        hintButton.setOnClickListener {
           processHintButtonClick()
        }
        submitButton.setOnClickListener {
            processSubmitButtonClick()
            quizViewModel.moveToNext()
        }
        refreshView()
    }

   private fun processAnswerButtonClick(answerIndex: Int) {    
       var answerList = quizViewModel.currentQuestionAnswer
        val answer = answerList[answerIndex]
        answerList.minus(answer).forEach { it.isSelected = false } //deselect all answers
        answer.isSelected = !answer.isSelected //toggle clicked button
        // refresh the view
        refreshView()
    }

    private fun processHintButtonClick() {
        // disable first enabled incorrect answer (even if selected)
        var answerList = quizViewModel.currentQuestionAnswer
        val incorrectAnswer = answerList.first {it.isEnabled && !it.isCorrect}
        incorrectAnswer.isEnabled = false
        incorrectAnswer.isSelected = false
        refreshView()
    }

    private fun processSubmitButtonClick() {
        var answerList = quizViewModel.currentQuestionAnswer    
        val correctAnswer = answerList.first { it.isSelected }
        if (correctAnswer.isCorrect) {
            Toast.makeText(this, R.string.correct_toast, Toast.LENGTH_SHORT).show()
        } else {
            Toast.makeText(this, R.string.incorrect_toast, Toast.LENGTH_SHORT).show()
        }

        for( it in answerList) {
                it.isEnabled = true
                it.isSelected = false
        }

        refreshView()
    }

    private fun refreshView() {

        var currentQuestionIndex = 0
        currentQuestionIndex++

        var question = quizViewModel.currentQuestionIndex
        var answerList = quizViewModel.currentQuestionAnswer

        questionTextView.setText(question)
        for((answer, button) in answerList.zip(answerButtonList)){
            button.setText(answer.textResId)
        }

        hintButton.setText(R.string.hint_button_text)
        submitButton.setText(R.string.submit_button_text)

        for ((answer, button) in answerList.zip(answerButtonList)) {
            button.isEnabled = answer.isEnabled
           button.isSelected = answer.isSelected

            if (answer.isSelected) {
                setButtonColor(button, selectedButtonColor)
            } else {
                setButtonColor(button, defaultButtonColor)
            }
            if (!answer.isEnabled) {
                button.alpha = .5f
            }
        }
        hintButton.isEnabled = answerList.any {it.isEnabled && !it.isCorrect}
        submitButton.isEnabled = answerList.any {it.isSelected}    
    }

    private fun setButtonColor(button: Button, colorString: String) {
        button.backgroundTintList =
            ColorStateList.valueOf(Color.parseColor(colorString))
        button.setTextColor(Color.WHITE)
        button.alpha = 1f
    }
}