NSCFSet objectAtIndex unrecognized selector, iterating works

I was wondering how it can be that iterating through an NSMutableArray works, but when I call objectAtIndex it fails with "*** -[NSCFSet objectAtIndex:]: unrecognized selector sent to instance 0x..."

Here is some sample code, the program is too big to share in whole so I hope it's enough. The code is executed in the latest iPhone Simulator from XCode.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
 RDLogString(@"Creating cell @ row no. %d", indexPath.row);
 CPPlayerAppDelegate * appDelegate = [[UIApplication sharedApplication] delegate];
 RDLogString(@"Conversations: %p. Item count: %d", appDelegate.distribution.conversations, appDelegate.distribution.conversations.count);  
 //This works  
 for(CPConversation * x in appDelegate.distribution.conversations){
  RDLog开发者_Go百科String(@"Pointer: %p with name %@", x, x.name);
 }  
 //This fails with aforementioned error  
 CPConversation * conversationAtCurrentIndex = [appDelegate.distribution.conversations objectAtIndex: indexPath.row];

Sorry for the bad formatting, still figuring it out. :)

Thanks in advance, Nick

objectAtIndex: is part of NSArray, not NSSet. This means your appDelegate.distribution.conversations is returning an NSSet and you need an NSArray.

That exception message is telling you that you're sending a message with a selector that the receiving class doesn't recognize or respond to. In this case, you're sending a objectAtIndex: message to an object of type NSCFSet (or just NSSet).

This means that whatever appDelegate.distribution.conversations is, you're expecting it to be an NSArray, but its actually an NSSet. How are you creating the object accessed there?