Collection was modified; enumeration operation may not execute in ArrayList [duplicate]

Question

I'm trying to remove an item from an ArrayList and I get this Exception:
Collection was modified; enumeration operation may not execute.

Any ideas?

Answer 1

You are removing the item during a foreach, yes? Simply, you can't. There are a few common options here:

• use List<T> and RemoveAll with a predicate

• iterate backwards by index, removing matching items

  for(int i = list.Count - 1; i >= 0; i--) {     if({some test}) list.RemoveAt(i); } 

• use foreach, and put matching items into a second list; now enumerate the second list and remove those items from the first (if you see what I mean)

Answer 2

Here's an example (sorry for any typos)

var itemsToRemove = new ArrayList();  // should use generic List if you can  foreach (var item in originalArrayList) {   if (...) {     itemsToRemove.Add(item);   } }  foreach (var item in itemsToRemove) {   originalArrayList.Remove(item); } 

OR if you're using 3.5, Linq makes the first bit easier:

itemsToRemove = originalArrayList   .Where(item => ...)   .ToArray();  foreach (var item in itemsToRemove) {   originalArrayList.Remove(item); } 

Replace "..." with your condition that determines if item should be removed.