Modify a dictionary which I am iterating through.

Question

foreach(BruteforceEntry be in Entries.Values)
{
    if (be.AddedTimeRemove <= now)
        Entries.Remove(be.IPAddress);
    else if (be.Unbantime <= now && be.Unbantime.Day == DateTime.Now.Day)
        Entries.Remove(be.IPAddress);
}

An exception was thrown: Collection was modified; enumeration operation may not execute. For some reason, it is not anymore.

EDIT: I know you cannot remove something, while iterating through it this way, my question is hhow do I solve it?

Answer 1

You can't modify the collection when iterating over it with foreach. Instead, iterate over it with a for loop.

Answer 2

You can't modify a collection you're iterating over. In this case, a much better solution would be to create a list of entries to remove by iterating over the dictionary, and then iterate over that list, removing the entries from the dictionary:

List<string> removals = new List<string>();                    
DateTime now = DateTime.Now;
foreach(BruteforceEntry be in Entries.Values)
{
    if (be.AddedTimeRemove <= now ||
        (be.Unbantime <= now && be.Unbantime.Day == DateTime.Now.Day))
    {
        removals.Add(be.IPAddress);
    }
}
foreach (string address in removals)
{
    Entries.Remove(address);
}

Note that if you're using .NET 3.5, you could use a LINQ query to express the first part:

List<string> removals = (from be in Entries.Values
                         where be.AddedTimeRemove <= now ||
                               (be.Unbantime <= now && 
                                be.Unbantime.Day == DateTime.Now.Day)
                         select be.IPAddress).ToList();

Answer 3

You can change foreach(BruteforceEntry be in Entries.Values) to foreach(BruteforceEntry be in new List<BruteforceEntry>(Entries.Values))

That way you don't modify your collection, but rather a copy of it.

Answer 4

Boiling down your problem...

foreach(... ... in Entries.Values)
{
        Entries.Remove(...);

}

As the others have said you are modifying the iterator while iterating.

You can, as @David said, use a for loop instead, but make sure to start at the end (reverse iteration).

Answer 5

Simply you can't remove an entry while you iterate on it.

Just as an example of workaround you can iterate over a shallow copy of the collection:

foreach(BruteforceEntry be in Entries.Values.ToList())
{
 ....
}

Answer 6

It looks like your question is about why an exception is not being thrown where it used to be. As the other answers state, you generally cannot change a collection through which you are iterating, but you are iterating over the Values collection, which, I believe, is a copy of the values in the dictionary, rather than referring to the main dictionary collection itself. So it no longer has the problem of iterating and modifying the same thing.

Answer 7

This (in my opinion) is the easiest way:

Dictionary<String, String> A = new Dictionary<string, string>(); //Example Dictionary
A.Add("A", "A"); //Example Values
A.Add("B", "B");
A.Add("C", "C");

for (int i = A.Count - 1; i >= 0; i--) //Loop backwards so you can remove elements.
{
     KeyValuePair<String, String> KeyValue = A.ElementAt(i); //Get current Element.
     if (KeyValue.Value == "B") A.Remove(KeyValue.Key);
}

In your case:

for (int i = Entries.Count - 1; i >= 0; i--)
{
    KeyValuePair<String, BruteforceEntry> KeyValue = Entries.ElementAt(i);
    if (KeyValue.Value.AddedTimeRemove <= now)
         Entries.Remove(KeyValue.Key);
    else if (KeyValue.Value.Unbantime <= now && KeyValue.Value.Unbantime.Day == DateTime.Now.Day)
         Entries.Remove(KeyValue.Key);
}