How to copy List without affecting first List

Question

I try copy a list, but when I change the second list, the first list is changed with the second list.

My model class:

public class urunler : ICloneable
{
public int id { get; set; }
public string icerik { get; set; }
}

Extensions class:

using System.Collections.Generic;
using System;
using System.Linq;

namespace Extensions
{
    public static class Extensions {

        public static IList<T> Clone<T>(this IList<T> SourceList) where T: ICloneable
        {
            return SourceList.Select(item => (T)item.Clone()).ToList();
        }
    }
}

BLL class:

using System.Linq;
using Extensions;
public class bll
{
    public void examp
    {
        List<urunler> L1 = new List<urunler>();
        urunler U = new urunler();
        U.icerik="old";
        L1.Add(U);
        List<urunler> L2 = L1.Clone();
        L2[0].icerik="new";
        MessageBox.show(L1[0].icerik);
        MessageBox.show(L2[0].icerik);
        //
    }
}

Error:

error CS0535: `urunler' does not implement interface member `System.ICloneable.Clone()'

And then I try change model class:

public class urunler : ICloneable
{
    #region ICloneable implementation

    IList<urunler> ICloneable.Clone()
    {
        throw new NotImplementedException ();
    }

    #endregion
    public int id { get; set; }
    public string icerik { get; set; }
}

error:

error CS0539: `System.ICloneable.Clone' in explicit interface declaration is not a member of interface

It works this time, I changed my model class

public class urunler : ICloneable
{
    public object Clone()         
    {             
        return this.MemberwiseClone();         
    }
    public int id { get; set; }
    public string icerik { get; set; }
}

And changed my bll class:

//before:
//List<urunler> L2 = L1.Clone();
//after:
List<urunler> L2 = L1.Clone().toList();

You are copying references. Use clone method or CopyTo method or ctor with old list list to create an in dependent list based on an original. — icbytes, May 12 '14 at 12:43
Answered many times http://stackoverflow.com/a/222623/125740 — Yahya, May 12 '14 at 12:44
You have too clone the list. Look at this http://stackoverflow.com/questions/222598/how-do-i-clone-a-generic-list-in-c. — Tan, May 12 '14 at 12:45
It's funny that you commented out `//or L2.AddRange(L1);` because that would've worked. — Rik, May 12 '14 at 12:50
possible duplicate of [How create a new deep copy (clone) of a List?](http://stackoverflow.com/questions/14007405/how-create-a-new-deep-copy-clone-of-a-listt) — huMpty duMpty, May 12 '14 at 16:03

score 1 · Answer 1 · answered May 12 '14 at 12:44

1

You're not copying a list, you're making a new reference to the same list. To copy a List, try this:

List<urunler> L2 = new List<urunler>(L1);

answered May 12 '14 at 12:44

Rik

28,507
14
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Dave Bish · Answer 2 · 2014-05-12T13:35:51.000

1

You can just use ToList() to create a copy / new list

var L2 = L1.ToList();

If you wish to create a new list, and create copies of the individual list-items, you will need to add a 'Clone' method to your object definition:

public class urunler : ICloneable
{
    public Object Clone()
    {
        return this.MemberwiseClone();
    }
}

Then:

var L2 = L1.Select(item => (urunler)item.Clone()).ToList();

edited May 12 '14 at 13:35

answered May 12 '14 at 12:53

Dave Bish

19,263
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I try but don't create new list. problem is contineu :( – user1811872 May 12 '14 at 13:17

Ehsan Sajjad · Accepted Answer · 2014-05-12T14:34:21.960

0

you can write your Extension Method for it:

public static class Extensions
{
    public static IList<T> Clone<T>(this IList<T> SourceList) where T: ICloneable
    {
        return SourceList.Select(item => (T)item.Clone()).ToList();
    }
}

use like this:

List<urunler> L2 = L1.Clone();

Your class:

public class urunler : ICloneable 
{ 
public int id { get; set; } 
public string ismi { get; set; } 
public string icerik { get; set; }

 public object Clone()
    {
        return this.MemberwiseClone();
    } 

}

edited May 12 '14 at 14:34

answered May 12 '14 at 12:43

Ehsan Sajjad

61,834
16
105
160

`CopyTo` copies to an array, not a `List` – Rik May 12 '14 at 12:45
I try, but don't work myclass name ex:urunler `List str = new List().Clone() //is work, List urun = new List().Clone() // is not work, expansion does not come after the dot` – user1811872 May 12 '14 at 13:45
put public with class – Ehsan Sajjad May 12 '14 at 13:46
myclass is public. `public class urunler { public int id { get; set; } public string ismi { get; set; } public string icerik { get; set; } }` – user1811872 May 12 '14 at 13:50
add public to extensions class – Ehsan Sajjad May 12 '14 at 13:51
See the update also you need to inherit urunler from IClonable:``public class urunler:ICloneable`` – Ehsan Sajjad May 12 '14 at 14:01
I couldn't =)) `error CS0535: urunler does not implement interface member System.ICloneable.Clone()` I try add interface but I couldn't again :D – user1811872 May 12 '14 at 14:12
add this in the class:``public object Clone() { return this.MemberwiseClone(); }`` – Ehsan Sajjad May 12 '14 at 14:34
see edited post as well, this time i tested on my system in a sample project its working – Ehsan Sajjad May 12 '14 at 14:34

Dennis_E · Answer 4 · 2014-05-12T12:54:07.350

0

L2=L1 Here's the mistake. L2 is referencing the same List as L1. You need to make a new List and copy the items:

L2 = new List<urunler>();
L1.CopyTo(L1);
//Edit: the above is wrong
L2 = new List<urunler>(L1);

edited May 12 '14 at 12:54

answered May 12 '14 at 12:44

Dennis_E

8,751
23
29

`CopyTo` copies to an array, not a `List` – Rik May 12 '14 at 12:46
I did try, but have a error. I change `L1.CopyTo(L1.toArray());` but it's not do that I want – user1811872 May 12 '14 at 13:15
L2 = new List(L1) is the correct way to go – Dennis_E May 12 '14 at 13:18

Jeppe Stig Nielsen · Answer 5 · 2014-05-12T14:22:40.833

Your type urunler appears to be a class, hence a reference type. Can you show us the definition of the urunler class, please?

Therefore, even when you clone the list correctly, you still produce a shallow clone. The two distinct List<> instances will have references to the same instance of urunler.

When you do L2 = L1;, you don't even clone the List<>. You just have two references to the same List<>, so that goes wrong at an early stage.

When you do L2 = new List<urunler>(L1); or L2 = L1.ToList(); or L2 = new List<urunler>(); L2.AddRange(L1);, you get the shallow copy I described. There are two distinct lists of references, but they refer to the same urunler instance.

Consider the cloning solution of the edited version of Dave Bish's answer.

Depending of your semantics, you could also make urunler an immutable type. Then instead of stuff like:

L2[0].icerik = "new";

you would have to do:

L2[0] = new urunler { icerik = "new", OtherProp = L2[0].OtherProp, };

etc.

How to copy List without affecting first List

5 Answers5