Why there is dependencies when i copy a List in a List>?

Question

I'm creating a little C# apps using List of an object and i have a very noob question :

First i'm filling my object 'A' , then i add in my list named 'lstA' :

List<List<A>> Lst_LstA = new List<List<A>>();  // List of List<A>
List<A> lstA = new List<A>(); // List of my object <A>

A myA = new A();
A.xxx = xx;
A.yyy = yy;

lstA.Add(A);
Lst_LstA.Add(lstA);
lstA.Clear();

What is my problem ? Very simple : When i call lstA.Clear(), it clear my lstA list, perfect, but...it clear too the element in my lst_LstA<> list.

I need to clear the lstA List, but only these list.

Why the Clear() modify too the other list ? How solve this simply ?

Thanks a lot,

best regards,

It's because `List<>` is a reference type... If you want to add it as new List, use `.Add(new List<>(a)`. Or use `.ToList()` — TripleEEE, Dec 05 '16 at 14:04

score 2 · Answer 1 · answered Dec 05 '16 at 14:04

2

The issue is that when you add lstA to lst_lstA, you're adding by reference - i.e. you're just adding a pointer to the list.

The only way for this to work would be to add a copy of lstA to lst_lstA

answered Dec 05 '16 at 14:04

simonalexander2005

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Perfect ! I did .Add(new List<>(a) and it's ok ! Thanks a lot ! – Walter Fabio Simoni Dec 05 '16 at 14:06
@WalterFabioSimoni no problem :) don't forget to mark it as the answer in a couple of hours' time, when it lets you – simonalexander2005 Dec 05 '16 at 14:11

Why there is dependencies when i copy a List in a List>?

1 Answers1