When I made NSCollectionView UI...
First time, I registered my collection view item class using
self.cv.register(NSNib.init(nibNamed: "ContentItemOneClass", bundle: nil), forItemWithIdentifier: "ContentItemOneClass")
and I added more collection views and forget to call like
self.cv.register(NSNib.init(nibNamed: "ContentItemTwoClass", bundle: nil), forItemWithIdentifier: "ContentItemTwoClass")
but collectionView(_:itemForRepresentedObjectAt:) , makeItem(withIdentifier:"ContentItemTwoClass", for: indexPath) seems to work just fine.
Now I wonder if registering classes is necessary or can be removed.
thanks.