Kotlin中包含对象的列表的深度副本

发布于07月23日

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)

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

这是因为您正在将所有对象引用添加到另一个列表中，因此您没有制作正确的副本，两个列表中有相同的元素.如果需要不同的列表和不同的引用，则必须克隆新列表中的每个对象:

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)]