Room 库无法识别 TypeConverter
我为 List
创建的枚举。但是,当我将其更改为 ArrayList
枚举它工作正常。任何人都知道为什么以及我可以做些什么来使用 List
? (在 Kotlin 中使用 List 更容易,我真的不想仅仅因为这个而前后转换为 ArrayList
)。
这是我的代码:
我的模特:
@Entity
data class Example(@PrimaryKey val id: String?,
val name: String,
var days: List<DayOfWeek>?)
DayOfWeek
是一个枚举:
enum class DayOfWeek {
MONDAY,
TUESDAY,
WEDNESDAY,
THURSDAY,
FRIDAY,
SATURDAY,
SUNDAY;
val value: Int
get() = ordinal + 1
companion object {
private val ENUMS = DayOfWeek.values()
fun of(dayOfWeek: Int): DayOfWeek {
if (dayOfWeek < 1 || dayOfWeek > 7) {
throw RuntimeException("Invalid value for DayOfWeek: " + dayOfWeek)
}
return ENUMS[dayOfWeek - 1]
}
}
}
我的TypeConverter
:
private const val SEPARATOR = ","
class DayOfWeekConverter {
@TypeConverter
fun daysOfWeekToString(daysOfWeek: List<DayOfWeek>?): String? {
return daysOfWeek?.map { it.value }?.joinToString(separator = SEPARATOR)
}
@TypeConverter
fun stringToDaysOfWeek(daysOfWeek: String?): List<DayOfWeek>? {
return daysOfWeek?.split(SEPARATOR)?.map { DayOfWeek.of(it.toInt()) }
}
}
我在我的数据库类中这样设置它:
@Database(entities = arrayOf(Example::class), version = 1)
@TypeConverters(DayOfWeekConverter::class)
abstract class AppDatabase : RoomDatabase() {
abstract fun exampleDao(): ExampleDao
}
我的 DAO 如下所示:
@Dao
interface ExampleDao {
@Query("SELECT * FROM example")
fun getAll(): LiveData<List<Example>>
@Insert(onConflict = REPLACE)
fun save(examples: List<Example>)
}
我使用此代码得到的错误是:
error: Cannot figure out how to save this field into database. You can consider adding a type converter for it.
e:
e: private java.util.List<? extends com.example.DayOfWeek> days;
如上所述,如果我更改 days
属性(property)到ArrayList<DayOfWeek>
(并对 ArrayList
中的 DayOfWeekConverter
进行更改)然后一切正常。如果有人能帮我解决这个问题并告诉我如何使用 List
在这里它会很有帮助,它让我发疯:/。
最佳答案
出于某种原因,Room 不喜欢 Kotlin List
,但是当我将 List
替换为 MutableList
时,它开始工作了:
@Entity
data class Example(@PrimaryKey val id: String,
val name: String,
var days: MutableList<DayOfWeek>?)
class DayOfWeekConverter {
companion object {
@TypeConverter
@JvmStatic
fun daysOfWeekToString(daysOfWeek: MutableList<DayOfWeek>?): String? =
daysOfWeek?.map { it.value }?.joinToString(separator = SEPARATOR)
@TypeConverter
@JvmStatic
fun stringToDaysOfWeek(daysOfWeek: String?): MutableList<DayOfWeek>? =
daysOfWeek?.split(SEPARATOR)?.map { DayOfWeek.of(it.toInt()) }?.toMutableList()
}
}
这不是完美的解决方案,但希望您可以对此进行更多调查。
您还需要将 @PrimaryKey
更改为不可为空
关于Android 房间错误 : TypeConverter not recognised for List of Enums,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/46785534/