Kotlin .add overriding all items of list in MutableList - object

Question

I have an object which contains a Mutable List
object TrackingEventsList {
var EventDate: String = ""
var EventDescription: String = ""
}
object Waybill {
var WaybillNumber: String = ""
var OriginHub: String = ""
var TrackingEvents: MutableList<TrackingEventsList> = ArrayList()
}
When I try to add Waybill.TrackingEvents all previous instances are overwritten to and duplicate the last TrackingEvent added.
private fun fillTracking(events: NodeList) {
var list = TrackingEventsList
for (x: Int in 0 until events.length) {
var tName = (events.item(x) as Element).tagName
var event = (events.item(x).firstChild as Text).wholeText
if (tName == "EventDate") {
list.EventDate = event
}
if (tName == "EventDescription") {
list.EventDescription = event
}
}
Waybill.TrackingEvents.plus(list)
}
The result after calling fillTracking 3 times:
Waybill.TrackingEvents[0].EventDescription = "Event3"
Waybill.TrackingEvents[1].EventDescription = "Event3"
Waybill.TrackingEvents[2].EventDescription = "Event3"

Answer 1

object in Kotlin is a singleton, which means you can't initialize it, and it only has one instance globally. So when you change the items of a single instance, you will override the previous data.
You should change both of them (or at least TrackingEventsList) to class instead. If Waybill's variables are instance-sensitive, it needs to be a class too. But in the code you added, I couldn't find anything that would say you use it as a singleton, so I left it as one.
class TrackingEventsList (
var eventDate: String = "",
var eventDescription: String = "")
/**
* Also want to point out that this is still a singleton. If the data inside is instance-specific, you need to change it
* to a class.
*/
object Waybill {
var waybillNumber: String = ""
var originHum: String = ""
var trackingEvents: MutableList<TrackingEventsList> = ArrayList()
}
private fun fillTracking(events: NodeList) {
val item = TrackingEventsList()
for (x: Int in 0 until events.length) {
var tName = (events.item(x) as Element).tagName
var event = (events.item(x).firstChild as Text).wholeText
if (tName == "EventDate") {
item.eventDate = event
}
if (tName == "EventDescription") {
item.eventDescription = event
}
}
Waybill.trackingEvents.add(item)
}
And you should look into the naming conventions for Kotlin; fields never start with an upper-case letter, unless it's a static constant (in which case it's all-upper)

Answer 2

Since TrackingEventsList is an object, it means it's a singleton (or only has a single instance.) When you go through your loop, you're always updating the same instance of your TrackingEventsList object.
Change TrackingEventsList to be this:
data class TrackingEventsList(var eventDate: String, var eventDescription: String)
Create a new instance each time you go through your loop, and then add it to your list at the end:
private fun fillTracking(events: NodeList) {
var eventDate: String = ""
var eventDescription: String = ""
for (x: Int in 0 until events.length) {
val tName = (events.item(x) as Element).tagName
val event = (events.item(x).firstChild as Text).wholeText
if (tName == "EventDate") {
eventDate = event
}
if (tName == "EventDescription") {
eventDescription = event
}
}
Waybill.TrackingEvents.plus(TrackingEventsList(eventDate, eventDescription))
}