Question

What is the bug here?

private void LoadUsers(List<long> uids, EventUser.EventUserStatus eventUserStatus, IList<user> chkfriends)
{
    foreach (var f in chkfriends) 
    {
      long l = f.uid; <-- fails
       if (uids.Contains(l)) do it!
    }

Error 1 Cannot implicitly convert type ‘long?’ to ‘long’. An explicit conversion exists (are you missing a cast?)

Answer 1

f.uid is presumably long? – in which case just:

long l = f.uid.Value;

This assumes that the value of uid isn’t empty. If there might be null ids in the set, then perhaps:

if(f.uid != null && uids.Contains(f.uid.Value)) {
    // do it!
}