Changing collection inside foreach

Question

Here is my code:

foreach (OrderItem item in OrderInfo.order)
{
     orderItemViews.Single(i => i.numericUpDown.Name == item.id.ToString()).numericUpDown.Value = item.count;
}

It gives an exception.
I know that I can't change the collection inside foreach
How can I change this code to make it work? Best of all if it would be LINQ code.

exception says that "The collection was modified". sorry can't provide real message of exception because it in non-english

sorry guys. I've found where collection is changing. It was inside *numericUpDown_ValueChanged* handler. anyway I've got an answer. thank you

when you changing your OrderInfo.order collection inside this loop? As i understood you just update your interface... — acrilige, Jan 19 '13 at 09:56
What's the exception? What is the type of orderItemViews, and what members does it have? — Eamon Nerbonne, Jan 19 '13 at 09:56
I see that OrderInfo.order is not changing. But I get this exception anyway. I don't know why — void, Jan 19 '13 at 10:10
In the code you have posted you are only making one assignment and that is not to the `OrderInfo.order` collection, we need to see more code. Is this nested inside another loop? — Grokodile, Jan 19 '13 at 10:14
Possible duplicate of [What is the best way to modify a list in a 'foreach' loop?](https://stackoverflow.com/questions/759966/what-is-the-best-way-to-modify-a-list-in-a-foreach-loop) — StayOnTarget, Jul 18 '18 at 11:55

score 8 · Accepted Answer · answered Jan 19 '13 at 09:57

8

You can use ToList(), Like this :

foreach (OrderItem item in OrderInfo.order.ToList())
{
     orderItemViews.Single(i => i.numericUpDown.Name == item.id.ToString()).numericUpDown.Value = item.count;
}

Or use normal for loop :

for (int i = 0 ; i < OrderInfo.order.Count; i++)
{
     OrderItem item = OrderInfo.order[i];
     orderItemViews.Single(i => i.numericUpDown.Name == item.id.ToString()).numericUpDown.Value = item.count;
}

Tip : Performance wise, It's better to use the second way.

answered Jan 19 '13 at 09:57

Shani Elharrar

667
4
5

2

Are you sure can this helped? Where are you see `odrer` collection changes? – Hamlet Hakobyan Jan 19 '13 at 09:59
@HamletHakobyan possibly, it is a side-effect in the `Value` setter -- we can't know without seeing the code. However, this is the solution for the enumerator invalidation problem. The `for` loop will solve that problem for sure. – Eren Ersönmez Jan 19 '13 at 10:04
@acrilige you don't know that. He may be changing the collection the `Value` setter. You can't know without seeing the full code. – Eren Ersönmez Jan 19 '13 at 10:09

score 2 · Answer 2 · answered Jan 19 '13 at 09:58

2

This is what I do, when I need to modify the collection.

foreach (OrderItem item in OrderInfo.order.ToList())
{
     ...
}

Create a copy. Enumerate the copy, but update the original one.

answered Jan 19 '13 at 09:58

Ondra

1,619
13
27

1

Are you sure can this helped? Where are you see `odrer` collection changes? – Hamlet Hakobyan Jan 19 '13 at 10:00

anefeletos · Answer 3 · 2017-11-26T01:27:02.343

0

You can use an extension ToEach static method:

public delegate void ToEachTransformAction<T>(ref T Telement);

[Extension()]
public static void ToEach<T>(Generic.IList<T> thislist, ToEachTransformAction<T> Transform)
    {
        for (var n = 0; n < thislist.Count; n++)
        {
            Transform.Invoke(thislist(n));
        }
    }

edited Nov 26 '17 at 01:27

answered Nov 25 '17 at 16:35

anefeletos

672
7
19

Changing collection inside foreach

3 Answers3

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