I try to clean/reset/clear a list in C# but it gives me InvalidOperationException error

Question

This is a part of an static int method:

int answer = 0;
foreach(int getal in savedNumbers)
{
    Console.WriteLine(getal);
    answer = answer + getal;
    savedNumbers.Clear(); // after this line, I'm getting an error.
}
return answer;

Please help me ... I don't know why savedNumbers.Clear() isn't working at that line.

EDIT: Thanks, problem is solved.

score 2 · Accepted Answer · answered Oct 14 '12 at 18:14

2

You can't modify the collection while enumerating over it. So, the exception is valid. Clear once you are done with enumerating it.

answered Oct 14 '12 at 18:14

Rohit Vats

79,502
12
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Can you accept the answer? Seems you need to work on it though. :) – Rohit Vats Oct 14 '12 at 18:33
Can you see the `right` checkmark besides the `upvote` number. Just click on that and it will be marked as an answer. – Rohit Vats Oct 14 '12 at 18:43

score 0 · Answer 2 · answered Oct 14 '12 at 18:13

0

You can't modify a list while iterating that same list.

answered Oct 14 '12 at 18:13

Alexandre Vinçon

919
5
13

score 0 · Answer 3 · answered Oct 14 '12 at 18:13

You are clearing the list in the middle of enumerating it. You cannot modify the list when you are in the process of enumeration.

int answer = 0;
foreach(int getal in savedNumbers)
{
    Console.WriteLine(getal);
    answer = answer + getal;
}
savedNumbers.Clear(); 
return answer;

score 0 · Answer 4 · edited May 23 '17 at 12:27

While iterating you cannot change the list/collection, while you can do the same using loop as stated below:

for (int i = 0 i < savedNumbers.Count; i++)
{
    var getal = savedNumbers[i];
    Console.WriteLine(getal);
    answer = answer + getal;
    savedNumbers.Clear();
}

You can't modify a collection while enumerating over it. That rule exists even without threading issues considered. From MSDN:

An enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and its behavior is undefined.

References:

score 0 · Answer 5 · answered Oct 14 '12 at 18:14

0

Msdn says: The foreach statement is used to iterate through the collection to get the desired information, but should not be used to change the contents of the collection to avoid unpredictable side effects

answered Oct 14 '12 at 18:14

Sanja Melnichuk

3,465
3
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I try to clean/reset/clear a list in C# but it gives me InvalidOperationException error

5 Answers5