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

Solution 1

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

Solution 2

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.

Comments

[lelloman]

have you tried somethinig?

[Pasha Shkaran]

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

[lelloman]

maybe it's worth mentioning it in your question

[LordRaydenMK]

I think the most relevant part here would be which converter are you using... GSON or something else?

[Pasha Shkaran]

@LordRaydenMK yes GSON

[LordRaydenMK]

have you tried using @SerializedName annotation? according to this stackoverflow.com/questions/25423590/enum-annotations-in-kot‌​lin it should work

[Blundell]

that's a GSON solution, change to @Json(name="foo") for moshi

[LordRaydenMK]

@ravidrinek please ask a new question, and include all relevant details, e.g. json parsing lib etc...

[Sergio]

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.