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

I would create two lists add into the second and then update the reference like this:

var urls = new List();
var destUrls = new List(urls);
urls.Add("http://www.google.com");
foreach (string url in urls)
{    
    // Get all links from the url    
    List newUrls = GetLinks(url);    
    destUrls.AddRange(newUrls);
}
urls = destUrls;