C#: Collection was modified; enumeration operation may not execute [duplicate]

Question

My goal is to delete a user from the user list in my application.But i cannot get to the bottom of this error. Some one plz bail me out.

if (txtEmailID.Text.Length > 0)
{
    users = UserRespository.GetUserName(txtEmailID.Text);
    bool isUserAvailable=false;
    foreach (EduvisionUser aUser in users) // Exception thrown in this line
    {
        isUserAvailable = true;
        if(!aUser.Activated)
        {
            users.Remove(aUser);
        }
    }
    if (users.Count == 0 && isUserAvailable)
    {
        DeactivatedUserMessage();
        return;
    }
}

Answer 1

You can't modify a collection while you're iterating over it with a foreach loop. Typical options:

• Use a for loop instead
• Create a separate collection of the items you want to act on, then iterate over that.

Example of the second approach:

List<EduvisionUser> usersToRemove = new List<EduvisionUser>();
foreach (EduvisionUser aUser in users) --->***Exception thrown in this line***
{
    isUserAvailable = true;
    if(!aUser.Activated)
    {
        usersToRemove.Add(aUser);
    }
}
foreach (EduvisionUser userToRemove in usersToRemove)
{
    users.Remove(userToRemove);
}

Another alternative, if you're using List<T> is to use List<T>.RemoveAll:

isUserAvailable = users.Count > 0;
users.RemoveAll(user => !user.Activated);