How to add items to a collection while consuming it?

Question

The example below throws an InvalidOperationException, \"Collection was modified; enumeration operation may not execute.\" when executing the code.

var urls         


        

Answer 1

Don't change the collection you're looping through via for each. Just use a while loop on the Count property of the list and access the List items by index. This way, even if you add items, the iteration should pick up the changes.

Edit: Then again, it sort of depends on whether you WANT the new items you added to be picked up by the loop. If not, then this won't help.

Edit 2: I guess the easiest way to do it would be to just change your loop to: foreach (string url in urls.ToArray())

This will create an Array copy of your list, and it will loop through this instead of the original list. This will have the effect of not looping over your added items.