Kotlin data class | add my own variables other than JSON keys

Question

I'm using retrofit and kotlin for my andorid app.

For one of my APIs, I have the following data classes

class Set(val set_id: Long, val tickets: List<Ticket>, val timer: Int) {}
class Ticket(val ticket_id: Long, val rows: List<Row>) {}
class Row(val row_id: Long, val row_numbers: List<Int>) {}

Sample JSON DATA

{
  "set_id": 60942,
  "tickets": [
    {
      "ticket_id": 304706,
      "rows": [
        {
          "row_id": 914116,
          "row_numbers": [
            0,
            11,
            21,
            0,
            42,
            52,
            0,
            76,
            85
          ]
        }
      ]
    }
  ],
  "timer": 12
}

Set class contains a list of Ticket and each ticket has a list of Row

My JSON object contains only these values and it is working fine till here. Retrofit mapping is also working.

Problem: I want to add my own a boolean field/variable isPlaying for class Ticket, which will be updated in the app later. But, this field should be set to true by default.

So I've tried this

class Ticket(val ticket_id: Long, val rows: List<Row>, var isPlaying: Boolean = true) {}

and this

class Ticket(val ticket_id: Long, val rows: List<Row>) {
    var isPlaying: Boolean = true
}

NOTE: JSON doesn't have isPlaying key, I want it for app logic only.

Both did not work, isPlaying is always showing false. I want it to be true by default.

Please, help me out. Thank you!

Answer 1

Default arguments would not work in data class in the case when objects are instantiated with retrofit due to parsing library used underneath, which probably creates objects without calling constructor. For example Gson uses sun.misc.Unsafeto create objects.

What you can do - is to add backing property for fields that have default values:

class Ticket(
    val ticket_id: Long, 
    val rows: List<Row>, 
    private var _isPlaying: Boolean? = true
) {
    var isPlaying
        get() = _isPlaying ?: true
        set(value) {
            _isPlaying = value
        }
}