Parsing a field in Kotlin, which can be a string or an object

Question

I encountered a problem when receiving data from the backend that the resulting field (for example, "somethingField") could be either a String or an Object with two Int lists. How can you parse such data correctly? I'm using kotlinx.serialization .

@Serializable
data class SomeObject(
    ...
    val somethingField: String or SometingObject
    ...
)

@Serializable
data class SomethingObject(
    val list1: List<Int>,
    val list2: List<Int>,
)

Answer 1

You can achieve this by using sealed classes. When the real type is one of the few available types, sealed classes are helpful in modeling constrained class hierarchies.

  import kotlinx.serialization.Serializable

  @Serializable
  sealed class SomethingField {
  @Serializable
  data class SomethingObject(val list1: List<Int>, val list2: List<Int>)             
  : SomethingField()

  @Serializable
  data class SomethingString(val value: String) : SomethingField()
  }


  @Serializable
  data class SomeObject(
  // ...
  val somethingField: SomethingField?,
  // ...
  )

You can then use it in your fragment or activity like this

  val someObject: SomeObject?  // ... deserialize from JSON

  when (someObject.somethingField) {
  is SomethingField.SomethingObject -> {
    // Handle SomethingObject case
    val list1 = someObject.somethingField.list1
    val list2 = someObject.somethingField.list2
  }
  is SomethingField.SomethingString -> {
    // Handle SomethingString case
    val stringValue = someObject.somethingField.value
  }
  }

This way, you can handle different cases based on the actual type of "somethingField".