How to put multiple objects in a mutableListOf in Kotlin?

Question

I'm trying to put some objects in a mutableListOf, but all of them ended up overriding.

class Users {...}

class dbUsers{
var users = Users()
val list = mutableListOf(users)

fun addUser(phone: Int, name: String){
    users.phone = phone
    users.name = name
    list.add(users)
}
}

fun main() {
var dbAccess = dbUsers()
dbAccess.addUser(8439, "Thiago")
dbAccess.addUser(12312, "Maria")
println(dbAccess.list[0].name)
println(dbAccess.list[1].name)
}

When We print at position 1, we see that was override

Upload the Users class as well

Karunesh Palekar
– Karunesh Palekar

2021-09-01 05:03:12 +00:00
Commented Sep 1, 2021 at 5:03 — Karunesh Palekar
– Karunesh Palekar, Commented Sep 1, 2021 at 5:03

sidgate · Accepted Answer · 2021-09-02 02:56:14Z

1

You have initialized Users object only once, at the class level in dbUsers. You need to create new object everytime before adding the user to the list. Move the users initialization within the method instead

class dbUsers{
   
   val list = mutableListOf<Users>()

   fun addUser(phone: Int, name: String){
     var users = Users()
     users.phone = phone
     users.name = name
     list.add(users)
   }
}

edited Sep 2, 2021 at 2:56

answered Sep 1, 2021 at 4:34

sidgate

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Comments

Anshul · Accepted Answer · 2021-09-01 03:56:39Z

It looks like the list is referencing from users and since users itself is updated every time, you get this results.

There are two ways you can approach this issue ,

Creating a new user every-time calling addUser , this is easy
If you have other data in Users than name and phone , you can just make a DeepCopy of your object by add in a new function in your class copy() like

class YourClass () {

// Your class other stuffs here

  fun copy(): YourClass { //Get another instance of YourClass with the values like this!
      val json = Gson().toJson(this)
      return Gson().fromJson(json, YourClass::class.java)
  }
}

then by using yourClassObject.copy() you will get a new instance with same values

fun addUser(phone: Int, name: String){
    val newUsers = users.copy()
    newUsers.phone = phone
    newUsers.name = name
    list.add(newUsers)
}

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