obj.m

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
    [layout prepareLayout];
    CGSize size = [layout collectionViewContentSize];
    CGRect rect = CGRectMake(0, 0, size.width, size.height);
    NSArray *layoutAttributes = [layout layoutAttributesForElementsInRect:rect];
    for (UICollectionViewLayoutAttributes *attributes in layoutAttributes) {
        switch (attributes.representedElementCategory) {
            case UICollectionElementCategoryCell:
                NSLog(@"Cell");
            break;
            case UICollectionElementCategorySupplementaryView:
                NSLog(@"Supplementary View");
            break;
            case UICollectionElementCategoryDecorationView:
                NSLog(@"Decoration View");
            break;
        }
        NSLog(@"Kind: %@", attributes.representedElementKind);
    }
});