How to get an instance of ViewModel

Question

I'm learning Kotlin from Java, and I'm trying to figure out how to create and store the ViewModel. Storing it outside the main activity will cause it to crash, but storing it inside the main activity means my private variables cannot access them, so I get an error.

Here's the code I have

class MainActivity : AppCompatActivity() {

    private lateinit var trueButton: Button
    private lateinit var falseButton: Button
    private lateinit var nextButton: Button
    private lateinit var prevButton: Button
    private lateinit var questionTextView: TextView


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val quizViewModel: QuizViewModel = ViewModelProvider(this).get(QuizViewModel::class.java)

        trueButton = findViewById(R.id.true_button)
        falseButton = findViewById(R.id.false_button)
        nextButton = findViewById(R.id.next_button)
        prevButton = findViewById(R.id.back_button)
        questionTextView = findViewById(R.id.question_text)


        trueButton.setOnClickListener {
            checkAnswer(true)
        }

        falseButton.setOnClickListener {
            checkAnswer(false)
        }

        nextButton.setOnClickListener {
            quizViewModel.moveToNext()
            updateQuestion()
        }

        prevButton.setOnClickListener {
            quizViewModel.moveToBack()
            updateQuestion()
        }

        updateQuestion()
    }

    private fun checkAnswer(userAnswer: Boolean){
        val correctAnswer = quizViewModel.currentQuestionAnswer
        val messageResId = if (userAnswer == correctAnswer) {
            R.string.correct_toast
        } else {
            R.string.incorrect_toast
        }
        Toast.makeText(
            this,
            messageResId,
            Toast.LENGTH_SHORT
        ).show()
    }

    private fun updateQuestion() {
        val questionTextResID = quizViewModel.currentQuestionText
        questionTextView.setText(questionTextResID)
    }


}

Unfortunately, putting the ViewModel inside my onCreate means I can't access them in my functions, namely checkAnswer and updateQuestion.

import androidx.lifecycle.ViewModel


class QuizViewModel : ViewModel() {
    private val questionBank = listOf(
        Question(R.string.question_aus, true),
        Question(R.string.question_ocean, true),
        Question(R.string.question_mideast, false),
        Question(R.string.question_africa, false),
        Question(R.string.question_america, true),
        Question(R.string.question_asia, true)
    )

    var currentIndex = 0

    val currentQuestionAnswer: Boolean
        get() = questionBank[currentIndex].answer
    val currentQuestionText: Int
        get() = questionBank[currentIndex].textResId

    fun moveToNext(){
        currentIndex = (currentIndex + 1) % questionBank.size
    }

    fun moveToBack(){
        currentIndex = (currentIndex - 1) % questionBank.size
    }
}

And my error

e: C:\Users\Jacob\AndroidStudioProjects\GeoQuiz\app\src\main\java\com\jacobjumper\geoquiz\MainActivity.kt: (54, 29): Unresolved reference: quizViewModel

Answer 1

just move the quizViewModel to the rest of the variables.

so like

class MainActivity : AppCompatActivity() {

    private lateinit var trueButton: Button
    private lateinit var falseButton: Button
    private lateinit var nextButton: Button
    private lateinit var prevButton: Button
    private lateinit var questionTextView: TextView
    private lateinit var quizViewModel: QuizViewModel


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        quizViewModel = ViewModelProvider(this).get(QuizViewModel::class.java)