Fragment class、MVVM、Viewmodel 中未解析的引用 (vars)

Question

我正在学习关于使用 Kotlin 开发 Android 应用程序的 UDACITY 免费课程，实际上我在课程的 Viewmodel/MVVM 部分，即实现视图模型 classes更好地分离关注点。所以无论如何，我现在被阻止了。我正在进行的练习是关于创建 Viewmodel class 并将变量和函数从 Fragment class 传输到这个新创建的 class。我一步一步地按照教程，在提供的 git diff 上检查正确答案，但我仍然发现自己被未解决的引用错误阻止了。

在更改代码之前，我必须更新我的 Gradle 模块文件以使用 ViewModel

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

然后我不得不在我的 Fragment 中声明我的 Viewmodel 对象 class

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

ViewModelProviders 被弃用，旧课程，我不得不在搜索后更改为

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

这似乎是正确的做法，但我仍然对变量 word (gameViewModel.word) 和 score (gameViewModel.score) 在 Fragment class 中，无法编译。我不知道我是否正确声明了 Viewmodel 对象，或者我是否遗漏了其他东西...

我没有这个问题，未解决的参考，我的 ViewModel class 函数，即 gameViewModel.onCorrect() 和 gameViewModel.onSkip()。它们似乎在片段 class 中被正确声明和调用，这让我对我的变量、单词和分数提出了问题...

我的片段class

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")
}
}

我的视图模型class

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()
}
}

我哪里搞砸了？

Answer 1

您尝试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() {
...

您的变量在 ViewModel 外部声明，将它们添加到 class GameViewModel 中以使其成为实例变量：

class GameViewModel: ViewModel() {
var word = ""
var score = 0
...
}

Fragment class、MVVM、Viewmodel 中未解析的引用 (vars)

Unresolved reference (vars) in Fragment class, MVVM, Viewmodel

android

kotlin

android-viewmodel