List collection was modified - Error when trying to use foreach loop

Question

I am trying to modify some values within the value of the List collection List<DataClass>. The value which I am trying to modify listValues[i].destinationValue and listValues[i].sourceKey which is also a list collection. When I am trying to add another value to the collection it works using foreach loop. But when it goes to next value in the foreach loop value it stops and I get the error: System.InvalidOperationException: 'Collection was modified;.

foreach (var listValue in listValues)
{
    if (listValue.hostName == data[4] && listValue.description == data[3] && listValue.ruleName == data[2])
    {
        var i = listValues.FindIndex(x => x.hostName.Equals(listValue.hostName));
        listValues[i].destinationValue.Add(data[0]);
        listValues[i].sourceKey.Add(data[1]);
    }
    else
    {
        listValues.Add(docValueModelClass);
    }
}

if (listValues.Count == 0)
{
    listValues.Add(docValueModelClass);
}

Can you please suggest, how can I overcome this?

Possible duplicate of [Collection was modified; enumeration operation may not execute in ArrayList](https://stackoverflow.com/questions/2024179/collection-was-modified-enumeration-operation-may-not-execute-in-arraylist) — Ňɏssa Pøngjǣrdenlarp, Aug 03 '19 at 19:32
`for (int i = 0; i < listValues.Count; ++i) { var listValue = listValues[i]; /* loop body here */ }` — Dmitry Bychenko, Aug 03 '19 at 19:36
change `foreach (var listValue in listValues)` to `foreach (var listValue in listValues.ToArray())`. Then your enumerate over a different list/array. — Frank Nielsen, Aug 03 '19 at 19:43
@DmitryBychenko: Using your suggestion worked perfect. Thanks for your help! — Dhillli4u, Aug 03 '19 at 19:51
@FrankNielsen: Thanks for pointing this out and very less code to modify and it works for me!!. Thanks a lot. — Dhillli4u, Aug 03 '19 at 19:52

logeshpalani31 · Accepted Answer · 2021-07-02T11:31:30.017

2

You can't edit same list or same enumerating list inside foreach loop, Because we using same list for enumerable.

just use for loop to edit - It works.

edited Jul 02 '21 at 11:31

answered Aug 03 '19 at 20:07

logeshpalani31

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List collection was modified - Error when trying to use foreach loop

1 Answers1