Question

I use asp.net 4, ef 4 in c#.
I use System.Web.Security to manage users in my web application.

I have a collection of users in MembershipUserCollection and I need remove some users during a foreach on that collector.

I suppose it is impossible to remove an item from the collector when you are looping.
Do you have any idea how to solve it?

Please provide me a sample of code, thanks!

       MembershipUserCollection users = Membership.GetAllUsers();
        foreach (MembershipUser x in users)
        {
            if (!Roles.IsUserInRole(x.UserName, "CMS-AUTHOR"))
            {
                users.Remove(x.UserName);
            }
         }

---

Error:

Collection was modified; enumeration operation may not execute. 

Answer 1

You can’t modify an enumeration while traversing it – put the users to remove in a list then remove all of them once you are done enumerating:

   MembershipUserCollection users = Membership.GetAllUsers();
   List<string> usersToRemove = new List<string>();
   foreach (MembershipUser x in users)
   {
        if (!Roles.IsUserInRole(x.UserName, "CMS-AUTHOR"))
            usersToRemove.Add(x.UserName);
   }
   foreach(string userName in usersToRemove)
         users.Remove(userName);

or shorter using LINQ:

var usersToRemove = Membership.GetAllUsers()
                              .Where( user => !Roles.IsUserInRole(user.UserName, "CMS-AUTHOR"))
                              .ToList();
usersToRemove.ForEach( user => users.Remove(user.UserName));