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

You can't, basically. What you really want here is a queue:

var urls = new Queue();
urls.Enqueue("http://www.google.com");

while(urls.Count != 0)
{
    String url = url.Dequeue();
    // Get all links from the url
    List newUrls = GetLinks(url);
    foreach (string newUrl in newUrls)
    {
        queue.Enqueue(newUrl);
    }
}

It's slightly ugly due to there not being an AddRange method in Queue but I think it's basically what you want.