从 SavedInstanceState 获取自定义类型列表时获取 IllegalStateException

Question

我有一个实现 Parcelable 的 Question 类，它充当 myquiz.db 和 dbHelper 类之间的桥梁。我要做的就是在设备旋转后恢复状态。这是 onSaveInstanceState() 中的代码：

override fun onSaveInstanceState(outState: Bundle?, outPersistentState: PersistableBundle?) {
        super.onSaveInstanceState(outState, outPersistentState)
        outState?.putInt(KEY_SCORE, score)
        outState?.putInt(KEY_QUES_COUNT, questionCounter)
        outState?.putBoolean(KEY_ANSWERED, answered)
        outState?.putLong(KEY_MILLIS_LEFT, timeLeftInMillis)
        outState?.putParcelableArrayList(KEY_QUES_LIST, list)
    }

这是我从 savedInstanceState 恢复列表的代码：

if (savedInstanceState == null) {
        val dbHelper = QuizDbHelper(this)
        list = dbHelper.getAllQuestions()
        totalQuestions = list.size
        list.shuffle()
        textDefaultColor = rb1.textColors
        textDefaultColorcd = timer.textColors
        nextQuestion()
    } else {
        **list = savedInstanceState.getParcelableArrayList(KEY_QUES_LIST)**
        totalQuestions = list.size
        score = savedInstanceState.getInt(KEY_SCORE)
        answered = savedInstanceState.getBoolean(KEY_ANSWERED)
        questionCounter = savedInstanceState.getInt(KEY_QUES_COUNT)
        currQuestion = list[questionCounter - 1]
        timeLeftInMillis = savedInstanceState.getLong(KEY_MILLIS_LEFT)

        if (!answered) {
            startTimer()
        } else {
            updateCoundownText()
            correctAnswer()
        }
    }

当我运行应用程序时，我收到此错误：java.lang.IllegalStateException: savedInstanceState.getPa…eArrayList(KEY_QUES_LIST) must not be null else 块中的第一行类型不匹配。此外，当我将鼠标指针悬停在这一行上时，它会显示：

Required:
ArrayList<Question>
Found:
ArrayList<Question!>?

列表声明：private lateinit var list: ArrayList<Question>

问题.class

class Question() : Parcelable {
private lateinit var question: String
private lateinit var option1: String
private lateinit var option2: String
private lateinit var option3: String
private var answerNr = 0

constructor(question: String, option1: String, option2: String, option3: String, answerNr: Int) : this() {
    this.question = question
    this.option1 = option1
    this.option2 = option2
    this.option3 = option3
    this.answerNr = answerNr
}

constructor(parcel: Parcel) : this() {
    parcel.readString()
    parcel.readString()
    parcel.readString()
    parcel.readString()
    parcel.readInt()
}


fun getQuestion(): String? {
    return question
}

fun setQuestion(question: String) {
    this.question = question
}

fun getOpt1(): String? {
    return option1
}

fun setOpt1(option1: String) {
    this.option1 = option1
}

fun getOpt2(): String? {
    return option2
}

fun setOpt2(option2: String) {
    this.option2 = option2
}

fun getOpt3(): String? {
    return option3
}

fun setOpt3(option3: String) {
    this.option3 = option3
}

fun getAnswerNo(): Int {
    return answerNr
}

fun setAnswerNo(answerNr: Int) {
    this.answerNr = answerNr
}

override fun writeToParcel(parcel: Parcel, flags: Int) {
    parcel.writeString(question)
    parcel.writeString(option1)
    parcel.writeString(option2)
    parcel.writeString(option3)
    parcel.writeInt(answerNr)
}

override fun describeContents(): Int {
    return 0
}

companion object CREATOR : Parcelable.Creator<Question> {
    override fun createFromParcel(parcel: Parcel): Question {
        return Question(parcel)
    }

    override fun newArray(size: Int): Array<Question> {
        return newArray(size)
    }
}

}

Answer 1

在 onSaveInstanceState 方法中，你是先调用 super 然后存储状态。所以 list 始终为 null 并且您已将列表声明为不可为 null，因此它会引发异常。

更新代码：

 override fun onSaveInstanceState(outState: Bundle?, outPersistentState: PersistableBundle?) {
            outState?.putInt(KEY_SCORE, score)
            outState?.putInt(KEY_QUES_COUNT, questionCounter)
            outState?.putBoolean(KEY_ANSWERED, answered)
            outState?.putLong(KEY_MILLIS_LEFT, timeLeftInMillis)
            outState?.putParcelableArrayList(KEY_QUES_LIST, list)
            super.onSaveInstanceState(outState, outPersistentState)
        }

Answer 2

问题在于如何定义list 以及如何从Bundle 恢复它。恢复保存的实例状态时，getParcelableArrayList() 的返回值可以为空。所以你的代码需要看起来像这样：

val restoredList = savedInstanceState.getParcelableArrayList(KEY_QUES_LIST)
restoredList?.also {
    list = it
}