java Realm 支持枚举吗？
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Enums support with Realm?
提问by MJB22
I'm working on an android app and Realm, and I need to create an enum attribute for one of my objects; but I discovered in this postthat Realm doesn't support enum yet.
我正在开发一个 android 应用程序和 Realm，我需要为我的一个对象创建一个枚举属性；但我在这篇文章中发现 Realm 还不支持枚举。
My object is like this:
我的对象是这样的：
public class ShuttleOption extends RealmObject {
private int Id;
private String Label;
private ShuttleTypes OriginShuttleType;
}
and my enum class (ShuttleTypes) corresponds with:
我的枚举类（ShuttleTypes）对应于：
HOME = 1;
and
和
WORK = 2;
Can anybody suggest me how to do it?
有人可以建议我怎么做吗？
回答by Christian Melchior
You can use the pattern described in the issue: https://github.com/realm/realm-java/issues/776#issuecomment-190147079
您可以使用问题中描述的模式：https: //github.com/realm/realm-java/issues/776#issuecomment-190147079
Basically save it as a String in Realm and convert it going in and out:
基本上将其保存为 Realm 中的 String 并将其转换为输入和输出：
public enum MyEnum {
FOO, BAR;
}
public class Foo extends RealmObject {
private String enumDescription;
public void saveEnum(MyEnum val) {
this.enumDescription = val.toString();
}
public MyEnum getEnum() {
return MyEnum.valueOf(enumDescription);
}
}
回答by Nicolás Carrasco
If you need a solution that works on Kotlin you can use the following:
如果您需要一个适用于 Kotlin 的解决方案，您可以使用以下方法：
open class Foo: RealmObject() {
var enum: MyEnum
get() { return MyEnum.valueOf(enumDescription) }
set(newMyEum) { enumDescription = newMyEnum.name }
private var enumDescription: String = MyEnum.FOO.name
}
MyEnumis the enum declared in @ChristianMelchior answer.
MyEnum是@ChristianMelchior 答案中声明的枚举。
It is worth mentioning that since enumdoesn't have a backing field,it won't be persisted into Realm. There is no need to use the @Ignoreannotation on it
值得一提的是，由于enum没有后台字段，所以不会持久化到Realm中。不需要在上面使用@Ignore注解
回答by Eric
i created a Kotlin delegate, which means a little less repitition
我创建了一个 Kotlin 委托，这意味着更少的重复
usage:
用法：
open class SomeDbModel : RealmObject() {
@delegate:Ignore
var variableEnum: MyEnum by enum(::variable)
private var variable: String = MyEnum.Default.name
}
delegate implementation:
委托实现：
package com.github.ericytsang
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KClass
import kotlin.reflect.KMutableProperty0
import kotlin.reflect.KProperty
inline fun <R, reified T : Enum<T>> enum(
backingField: KMutableProperty0<Int>
) = OrdinalToEnumDelegate<R, T>(T::class, backingField)
val <T : Enum<T>> KClass<out T>.enumValues get() = java.enumConstants!!.toList()
class StringToEnumDelegate<R, T : Enum<T>>(
/**
* enum class to convert the ordinal values in [backingField] to.
*/
enumClass: KClass<T>,
/**
* the property containing [T]'s ordinal value.
*/
private val backingField: KMutableProperty0<String>
) : ReadWriteProperty<R, T> {
private val enumValues = enumClass.enumValues.associateBy { it.name }
override fun getValue(thisRef: R, property: KProperty<*>): T {
return enumValues[backingField.get()]
?: error("no corresponding enum found for ${backingField.get()} in ${enumValues.keys}")
}
override fun setValue(thisRef: R, property: KProperty<*>, value: T) {
backingField.set(value.name)
}
}
