如何使用 Room 解析 kotlin android 开发中具有密封 class 参数的对象？

Question

I have a Plant data class, that has a PlantType sealed class parameter. I am using a Room local db, but when I try to parse it it fails. It works for other classes that has initializable class parameters.

Thanks for the help in advance.

The error:
java.lang.RuntimeException: Failed to invoke private com.tenyitamas.mylittlegarden.domain.util.PlantType() with no args

at com.tenyitamas.mylittlegarden.data.util.Converters.fromPlantsJson(Converters.kt:99)

// Comment: Converters.kt: 99 is the from json part of the Converters code, I included.

Plant.kt:

data class Plant(
    val type: PlantType,
    val upgrades: Upgrades
)

PlantType.kt:

sealed class PlantType {
    object Carrot : PlantType()
    object Tomato : PlantType()
    object Cucumber : PlantType()
    object Lettuce : PlantType()
    object Strawberry : PlantType()
}

Converters.kt

@TypeConverter
    fun fromPlantsJson(json: String): List<Plant> {
        return jsonParser.fromJson<ArrayList<Plant>>(
            json,
            object : TypeToken<ArrayList<Plant>>(){}.type
        ) ?: emptyList()
    }

    @TypeConverter
    fun toPlantsJson(plants: List<Plant>): String {
        return jsonParser.toJson(
            plants,
            object : TypeToken<ArrayList<Plant>>(){}.type
        ) ?: "[]"
    }

Answer 1

Your PlantType sealed class has only objects inside it. You can just use an enum for this.

enum class PlantType {
    Carrot, Tomato, Cucumber, Lettuce,  Strawberry
}

And most likely your jsonParser will be able to serialize this enum.