Kotlin 中对象列表的深拷贝 [英] Deep copy of list with objects in Kotlin

问题描述

我是 kotlin 的新手，我正在尝试制作对象列表的副本.我遇到的问题是，当我更改新副本中的项目时，旧列表也会更改.这是对象:

I am new to kotlin and I am trying to make a copy of a list of objects.The problem I am having is that when I change items in the new copy, the old list gets changed as well. This is the object:

class ClassA(var title: String?, var list: ArrayList<ClassB>, var selected: Boolean)
class ClassB(val id: Int, val name: String) 

我试过这样做，但它不起作用:

I tried doing this, but it doesn't work:

val oldList:ArrayList<ClassA>


val newList :ArrayList<ClassA> = ArrayList()
newList.addAll(oldList)

推荐答案

那是因为您将所有对象引用添加到另一个列表，因此您没有进行正确的复制，您在两个列表中有相同的元素.如果你想要不同的列表和不同的引用，你必须克隆一个新列表中的每个对象:

That's bacause you are adding all the object references to another list, hence you are not making a proper copy, you have the same elements in two list. If you want diferents list and diferent references, you must clone every object in a new list:

public data class Person(var n: String)

fun main(args: Array<String>) {
    //creates two instances
    var anna = Person("Anna")
    var Alex =Person("Alex")

    //add to list
    val names = arrayOf(anna , Alex)
    //generate a new real clone list
    val cloneNames = names.map{it.copy()}

    //modify first list
    cloneNames.get(0).n = "Another Anna clone"

    println(names.toList())
    println(cloneNames.toList())
}

[Person(n=Anna), Person(n=Alex)]
[Person(n=Another Anna clone), Person(n=Alex)]

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