How use Kotlin enum with Retrofit?

Question

How can I parse JSON to model with enum?

Here is my enum class:

enum class VehicleEnumEntity(val value: String) {
   CAR("vehicle"),
   MOTORCYCLE("motorcycle"),
   VAN("van"),
   MOTORHOME("motorhome"),
   OTHER("other")
}

and I need to parse type into an enum

"vehicle": { "data": { "type": "vehicle", "id": "F9dubDYLYN" } }

EDIT

I have tried standard way, just pass my enum to POJO and it always null

@lelloman yes, I have tried standard way, just pass my enum to POJO and it always null — Pasha Shkaran, Aug 07 '17 at 18:27
I think the most relevant part here would be which converter are you using... GSON or something else? — LordRaydenMK, Aug 07 '17 at 18:31
have you tried using @SerializedName annotation? according to this https://stackoverflow.com/questions/25423590/enum-annotations-in-kotlin it should work — LordRaydenMK, Aug 07 '17 at 18:34

score 92 · Accepted Answer · answered Aug 07 '17 at 18:41

92

enum class VehicleEnumEntity(val value: String) {
   @SerializedName("vehicle")
   CAR("vehicle"),

   @SerializedName("motorcycle")
   MOTORCYCLE("motorcycle"),

   @SerializedName("van")
   VAN("van"),

   @SerializedName("motorhome")
   MOTORHOME("motorhome"),

   @SerializedName("other")
   OTHER("other")
}

Source

answered Aug 07 '17 at 18:41

LordRaydenMK

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that's a GSON solution, change to `@Json(name="foo")` for moshi – Blundell Aug 14 '20 at 11:58
1

@ravidrinek please ask a new question, and include all relevant details, e.g. json parsing lib etc... – LordRaydenMK Aug 30 '20 at 12:17
How can I do it with `Int` instead of `String`? – Carlos Leonardo Camilo Vargas Feb 09 '23 at 01:03
@CarlosLeonardoCamiloVargas you change the String to an Int and make sure backend also returns an Int – LordRaydenMK Feb 10 '23 at 08:08
It works for me, Thanks – Hossein Kurd Aug 06 '23 at 09:06

score 16 · Answer 2 · answered Aug 08 '17 at 06:42

Another option: use a custom (de)serializer that uses the value of the enum, instead of the name (default). This means you don't need to annotate every enum value, but instead you can annotate the enum class (or add the adapter to GsonBuilder).

interface HasValue {
    val value: String
}

@JsonAdapter(EnumByValueAdapter::class)
enum class VehicleEnumEntity(override val value: String): HasValue {
   CAR("vehicle"),
   MOTORCYCLE("motorcycle"),
   VAN("van"),
   MOTORHOME("motorhome"),
   OTHER("other")
}

class EnumByValueAdapter<T> : JsonDeserializer<T>, JsonSerializer<T>
    where T : Enum<T>, T : HasValue {
    private var values: Map<String, T>? = null

    override fun deserialize(
        json: JsonElement, type: Type, context: JsonDeserializationContext
    ): T? =
        (values ?: @Suppress("UNCHECKED_CAST") (type as Class<T>).enumConstants
            .associateBy { it.value }.also { values = it })[json.asString]

    override fun serialize(
        src: T, type: Type, context: JsonSerializationContext
    ): JsonElement = JsonPrimitive(src.value)
}

The same adapter class is reusable on other enum classes.

This works nicely if the enum type is String. Is there a way to create a generic adapter for any type? The most common enum values are strings and integers I think, but it would be nice to have a generic way to serialize any type. — Sergio, Dec 08 '20 at 15:28

score 3 · Answer 3 · answered Feb 10 '23 at 16:20

In case the backend service responses integers for example. You can you change the constructor parameter as Int.

enum class Day(val rawValue: Int) {
    @SerializedName("1")
    SUNDAY(1),
    @SerializedName("2")
    MONDAY(2),
    @SerializedName("3")
    TUESDAY(3),
    @SerializedName("4")
    WEDNESDAY(4),
    @SerializedName("5")
    THURSDAY(5),
    @SerializedName("6")
    FRIDAY(6),
    @SerializedName("7")
    SATURDAY(7),
    @SerializedName("-1")
    UNSUPPORTED(-1);

    companion object {
        fun from(findValue: Int): Day = values().firstOrNull { it.rawValue == findValue } ?: UNSUPPORTED
    }
}

Nitpick: The from function helps you to find an enum value easily by a given Int.

How use Kotlin enum with Retrofit?

3 Answers3

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