Android 片段类、MVVM、Viewmodel中的未解析引用（VAR）

我正在学习UDACITY免费课程，学习如何使用Kotlin开发Android应用程序，实际上我正在学习课程的Viewmodel/MVVM部分，即实现Viewmodel类以更好地分离关注点。不管怎样，我现在被封锁了。我正在进行的练习是关于创建Viewmodel类，并将变量和函数从Fragment类传输到这个新创建的类。我一步一步地遵循教程，检查所提供git diff的正确答案，我仍然发现自己被未解决的引用错误阻塞

在更改代码之前，我必须更新Gradle模块文件以使用ViewModel

//ViewModel
implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'

然后我必须在片段类中声明Viewmodel对象

gameViewModel = ViewModelProviders.of(this).get(GameViewModel::class.java)

package com.example.android.guesstheword.screens.game

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.databinding.DataBindingUtil
import androidx.fragment.app.Fragment
import androidx.lifecycle.ViewModelProvider
import androidx.navigation.fragment.NavHostFragment.findNavController
import com.example.android.guesstheword.R
import com.example.android.guesstheword.databinding.GameFragmentBinding
import timber.log.Timber

class GameFragment : Fragment() {

private lateinit var binding: GameFragmentBinding

private lateinit var gameViewModel: GameViewModel



override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                          savedInstanceState: Bundle?): View? {

    // Inflate view and obtain an instance of the binding class
    binding = DataBindingUtil.inflate(
            inflater,
            R.layout.game_fragment,
            container,
            false
    )

    Timber.i("onCreateView  GameFragment called")
    gameViewModel = ViewModelProvider(this).get(GameViewModel::class.java)
    Timber.i("ViewModelProvider is called")

    binding.correctButton.setOnClickListener {
        gameViewModel.onCorrect()
        updateScoreText()
        updateWordText()
    }
    binding.skipButton.setOnClickListener {
        gameViewModel.onSkip()
        updateScoreText()
        updateWordText()
    }
    updateScoreText()
    updateWordText()
    return binding.root

}

/**
 * Called when the game is finished
 */
fun gameFinished() {
    val action = GameFragmentDirections.actionGameToScore(gameViewModel.score)
    findNavController(this).navigate(action)
}

/** Methods for updating the UI **/

private fun updateWordText() {
    binding.wordText.text = gameViewModel.word
}

private fun updateScoreText() {
    binding.scoreText.text = gameViewModel.score.toString()
}

override fun onDestroyView() {
    super.onDestroyView()
    Timber.i("onDestroyView GameFragment called")
}
}

ViewModelProviders已被弃用，旧课程，我必须在搜索后更改为

gameViewModel = ViewModelProvider(this).get(GameViewModel::class.java)

这似乎是正确的方法，但我仍然有一些关于Fragment类中变量word gameViewModel.word和score gameViewModel.score的未解析引用，无法编译。我不知道我是否正确声明了Viewmodel对象，或者是否缺少其他内容

我的ViewModel类函数（即gameViewModel.onCorrect和gameViewModel.onSkip）没有未解决的引用问题。它们似乎是在Fragment类中正确声明和调用的，这就向我提出了关于变量、单词和分数的问题

我的碎片类

gameViewModel = ViewModelProviders.of(this).get(GameViewModel::class.java)

package com.example.android.guesstheword.screens.game

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.databinding.DataBindingUtil
import androidx.fragment.app.Fragment
import androidx.lifecycle.ViewModelProvider
import androidx.navigation.fragment.NavHostFragment.findNavController
import com.example.android.guesstheword.R
import com.example.android.guesstheword.databinding.GameFragmentBinding
import timber.log.Timber

class GameFragment : Fragment() {

private lateinit var binding: GameFragmentBinding

private lateinit var gameViewModel: GameViewModel



override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                          savedInstanceState: Bundle?): View? {

    // Inflate view and obtain an instance of the binding class
    binding = DataBindingUtil.inflate(
            inflater,
            R.layout.game_fragment,
            container,
            false
    )

    Timber.i("onCreateView  GameFragment called")
    gameViewModel = ViewModelProvider(this).get(GameViewModel::class.java)
    Timber.i("ViewModelProvider is called")

    binding.correctButton.setOnClickListener {
        gameViewModel.onCorrect()
        updateScoreText()
        updateWordText()
    }
    binding.skipButton.setOnClickListener {
        gameViewModel.onSkip()
        updateScoreText()
        updateWordText()
    }
    updateScoreText()
    updateWordText()
    return binding.root

}

/**
 * Called when the game is finished
 */
fun gameFinished() {
    val action = GameFragmentDirections.actionGameToScore(gameViewModel.score)
    findNavController(this).navigate(action)
}

/** Methods for updating the UI **/

private fun updateWordText() {
    binding.wordText.text = gameViewModel.word
}

private fun updateScoreText() {
    binding.scoreText.text = gameViewModel.score.toString()
}

override fun onDestroyView() {
    super.onDestroyView()
    Timber.i("onDestroyView GameFragment called")
}
}

我的ViewModel类

package com.example.android.guesstheword.screens.game

import androidx.lifecycle.ViewModel
import timber.log.Timber

var word = ""
var score = 0

private lateinit var wordList: MutableList<String>

class GameViewModel: ViewModel() {
init {
    Timber.i("GameViewModel is created")
    resetList()
    nextWord()
}

override fun onCleared() {
    super.onCleared()
    Timber.i("GameViewModel is cleared")
}
/**
 * Resets the list of words and randomizes the order
 */


fun resetList() {
    wordList = mutableListOf(
            "queen",
            "hospital",
            "basketball",
            "cat",
            "change",
            "snail",
            "soup",
            "calendar",
            "sad",
            "desk",
            "guitar",
            "home",
            "railway",
            "zebra",
            "jelly",
            "car",
            "crow",
            "trade",
            "bag",
            "roll",
            "bubble"
    )
    wordList.shuffle()
}
/**
 * Moves to the next word in the list
 */
private fun nextWord() {
    //Select and remove a word from the list
    if (wordList.isEmpty()) {
        //gameFinished()
    } else {
        word = wordList.removeAt(0)
    }
}
/** Methods for buttons presses **/

fun onSkip() {
    score--
    nextWord()
}

fun onCorrect() {
    score++
    nextWord()
}
}

---

我在哪里搞砸了？

您试图访问的变量不属于同一范围：

var word = ""
var score = 0

private lateinit var wordList: MutableList<String>

class GameViewModel: ViewModel() {
...

---

您已在类外声明var word=和var score=0。把它放在课堂上，你就可以走了。