例外情况“收集已被修改”，但尚未修改

Question

I'm getting this exception with this code and can't understand why

private static void LoopBTCtx()
{
    Task.Factory.StartNew(async () =>
    {
        while (true)
        {
            try
            {
                Thread.Sleep((int)TimeSpan.FromSeconds(10).TotalMilliseconds);

                List<(string, SocketMessage, int)> _btcTX = btcTX;

                foreach (var tx in btcTX)
                {
                    int newConfirmations = GetBTCtxConfirmations(tx.Item1);

                    if (tx.Item3 != newConfirmations)
                    {
                        _btcTX.Remove(tx);

                        if (newConfirmations < 6)
                        {
                            _btcTX.Add((tx.Item1, tx.Item2, newConfirmations));
                        }

                        await tx.Item2.Channel.SendMessageAsync($"{tx.Item2.Author.Mention}, ``{tx.Item1}`` now has **{newConfirmations}**/6 confirmation{(newConfirmations != 1 ? "s" : null)}.");
                    }
                }

                btcTX = _btcTX;
            }
            catch (Exception e)
            {
                Console.WriteLine(e);
            }
        }
    });
}

It's thrown after processing the first list element ( foreach )

The exception line from the stacktrace is the one containing foreach (var tx in btcTX)

I tried using 2 different lists then updating the main one once the foreach is done, as you can see in my code above, but it didn't fix.

Answer 1

You still have one list. The following statement just causes _btcTX to point to the same list instance as btcTX:

List<(string, SocketMessage, int)> _btcTX = btcTX;

So actually the main list was modified in the Remove() and/or Add(). One way to remove/add the items is to perform a regular for loop with an index (from last to first), and then you will be able to remove/add items with no problem. Another way would be to keep the foreach loop, but store the indices to be removed and the items to be added inside the loop and then perform the actual adding/removal after the loop (removing should be done from the last index to the first).