Android 房间数据库 - 不确定如何将 Cursor 转换为此方法的返回类型

Question

我正在尝试将此对象保存在 Room 数据库中，我阅读了有关 Typeconverters 的信息，用于将复杂对象转换为可以存储在数据库中的一个字段。我收到此错误:
错误:不确定如何将 Cursor 转换为此方法的返回类型 (androidx.lifecycle.LiveData>).----
公共(public)抽象 androidx.lifecycle.LiveData> queryQuestions(@org.jetbrains.annotations.NotNull()
我的代码基于我发现的用于转换房间对象的类似问题的解决方案，但这对我不起作用。

我的问题类:

@Entity

    data class Question(@PrimaryKey var questionId: String = "",
                        val uid: String,
                        val name: String,
                        val photo: String,
                        val question: String,
                        val points: Int,
                        @ServerTimestamp val timestamp: Date? = null,
                        val options: ArrayList<Option>){
        constructor(): this("", "", "", "", "", 0, null, ArrayList())
    }

    data class Option(val optionText: String,
                      val correct: Boolean,
                      var votes: Int = 0,
                      var usersVoted: ArrayList<UserVoted> = ArrayList()){
        constructor(): this("", false /*,0, ArrayList()*/)
    }

    data class UserVoted(val name: String,
                         val photo: String){
        constructor(): this("", "")
    }

我的道课:

@Dao
interface QuestionDao {
    @Insert(onConflict = REPLACE)
    fun insertQuestions(question: ArrayList<Question>)

    @Query("SELECT * FROM question WHERE uid = :userId")
    fun queryQuestions(userId: String): LiveData<ArrayList<Question>>
}

我的数据库类:

@Database(entities = [Question::class], version = 1)
@TypeConverters(Converter::class)
abstract class AppDatabase : RoomDatabase(){
    abstract fun questionDao(): QuestionDao

}

我的转换器类:

class Converter {

    @TypeConverter
    fun fromTimestampToDate(value: Long?): Date? {
        return value?.let { Date(it) }
    }

    @TypeConverter
    fun fromDateToTimestamp(date: Date?): Long? {
        return date?.time?.toLong()
    }

    @TypeConverter
    fun fromStringToArrayList(value: String): ArrayList<Option> {
        Log.i("alengenije", "fromStringToArrayList string = $value")
        val listType = object:TypeToken<ArrayList<Option>>() {}.type
        return Gson().fromJson(value, listType)
    }

    @TypeConverter
    fun fromArrayLisrToString(list: ArrayList<Option>): String {
        val gson = Gson()
        return gson.toJson(list)
    }

}

Answer 1

更改ArrayList至List .

这个对我有用。