Room库无法识别我为TypeConverter
个枚举创建的List
。但是,当我将其更改为ArrayList
枚举时,它可以正常工作。任何人都知道为什么以及如何使用List
来完成这项工作? (在Kotlin中使用List更容易,我真的不想仅仅因为这个而转发回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DB类中设置它:
@Database(entities = arrayOf(Example::class), version = 1)
@TypeConverters(DayOfWeekConverter::class)
abstract class AppDatabase : RoomDatabase() {
abstract fun exampleDao(): ExampleDao
}
我的DAO看起来像这样:
@Dao
interface ExampleDao {
@Query("SELECT * FROM example")
fun getAll(): LiveData<List<Example>>
@Insert(onConflict = REPLACE)
fun save(examples: List<Example>)
}
我使用此代码获得的错误是:
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;
就像我上面所说,如果我将days
属性更改为ArrayList<DayOfWeek>
(并在ArrayList
中对DayOfWeekConverter
进行更改),那么一切正常。如果有人能帮助我解决这个问题并告诉我如何在List
使用<?xml version="1.0" encoding="utf-8"?>
<CheckedTextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@android:id/text1"
style="?android:attr/spinnerDropDownItemStyle"
android:singleLine="true"
android:layout_width="match_parent"
android:layout_height="?android:attr/dropdownListPreferredItemHeight"
android:ellipsize="marquee"
android:background="MY REQUIRED COLOR"/>
它会给你带来很大的帮助,它会让我发疯:/。
答案 0 :(得分:12)
出于某种原因,Room不喜欢Kotlin List
,但当我用List
取代MutableList
时,它开始起作用了:
@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,但希望你能用此进行更多调查。
此外,您需要将@PrimaryKey
更改为不可为空的
答案 1 :(得分:2)
在Kotlin中List
的完整签名是List<out E>
(在Java中是List<? extend E>
),转换这种通用类型没有任何意义。换句话说,Room不知道输入是DayOfWeek
还是它的子类。
对于ArrayList
和MutableList
,它们的完整签名分别为ArrayList<E>
和MutableList<E>
,输入类型是固定的,因此Room知道如何进行转换。
答案 2 :(得分:-1)
我们无法存储和获取没有数组列表的List枚举。房间不支持它。但是如果你想避免使用数组列表,你可以创建一个ListDayOfWeek对象,List是一个属性。我试过了,没关系。如果您需要代码,请在此处回复。我会发布它。
答案 3 :(得分:-1)
您不应该将其存储到数据库中。更好地构建类似的东西并将其存储为int:
enum class DaysOfWeek(var bitValue: Int) {
Monday(64),
Tuesday(32),
Wednesday(16),
Thursday(8),
Friday(4),
Saturday(2),
Sunday(1);
}
最后,您的实用程序可以从/转换为枚举。
fun daysToBitValue(days: EnumSet<DaysOfWeek>): Int {
var daysBitValue = 0
for (`val` in days) daysBitValue += `val`.bitValue
return daysBitValue
}
private fun fromBitValues(origBitMask: Int): EnumSet<DaysOfWeek> {
val ret_val = EnumSet.noneOf(DaysOfWeek::class.java)
var bitMask = origBitMask
for (`val` in DaysOfWeek.values()) {
if (`val`.bitValue and bitMask == `val`.bitValue) {
bitMask = bitMask and `val`.bitValue.inv()
ret_val.add(`val`)
}
}
if (bitMask != 0) {
throw IllegalArgumentException(String.format(Locale.getDefault(), "Bit mask value 0x%X(%d) has unsupported bits 0x%X. Extracted values: %s", origBitMask, origBitMask, bitMask, ret_val))
}
return ret_val
}
现在你可以存储一个int并在以后的工作日获得:
@Entity
data class Example(@PrimaryKey val id: String?,
val name: String,
var days: Int = 0)
或者你使用enum并为此编写一个合适的typeconverter。
@Entity
data class Example(@PrimaryKey val id: String?,
val name: String,
var days: EnumSet<DaysOfWeek>?)
class DayOfWeekConverter {
@TypeConverter
fun daysOfWeekToString(daysOfWeek: EnumSet<DayOfWeek>?) =
daysOfWeek?.let{ YourUtilities.daysToBitValue(it) }
@TypeConverter
fun intToDaysOfWeek(daysOfWeek: Int?) =
daysOfWeek?.let { YourUtilities.fromBitValues(it) }
}
您可以循环使用枚举,并使用
获取所有日期for (aDaysOfWeekEnumSet in daysOfWeekEnumSet)
info{ "day = ${aDaysOfWeekEnumSet.name"}
代码未经测试,因为我不在我的计算机上,但这应该显示更好的概念,然后存储枚举(这只是预定义值的别名!)