When something changes, post a notification, like

// send out notification so image list we’re from can display
NSDictionary* info = [NSDictionary dictionaryWithObjectsAndKeys:
[self.collection collectionController], ICListOwner,
[NSNumber numberWithInt:collectionIndex], ICImageIndex,
nil
];
[[NSNotificationCenter defaultCenter] postNotificationName:ICImageIndexChangedNotification object:self userInfo:info];

and in -viewDidLoad of the view you want to reflect a selection change, listen for it

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(displayedImageChanged:) name:ICImageIndexChangedNotification object:nil];

– and whenever you call addObserver, don’t forget to removeObserver in dealloc! –

[[NSNotificationCenter defaultCenter] removeObserver:self];

then write the function you declared in addObserver to do whatever it is you want. In this particular case I’m scrolling a thumbnail list to reflect that the image in the detail view was changed.

- (void)displayedImageChanged:(NSNotification*)notification
{
UINavigationController* controller = [[notification userInfo] objectForKey:ICListOwner];
if (self.navigationController != controller)
return;

NSNumber* imageIndexNumber = [[notification userInfo] objectForKey:ICImageIndex];
int imageIndex = [imageIndexNumber intValue];

int lineToShow = [appDelegate lineForGalleryIndex:imageIndex];
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:lineToShow inSection:0];
[libraryTableView scrollToRowAtIndexPath:indexPath
atScrollPosition:UITableViewScrollPositionMiddle
animated:NO
];
}

Would it be hard to put a UIImage in the detailview and having that image change based on the item selected. I think if you could modify it to do that, would be a great sample app that would teach a lot.