BlogCustomLayotElementsInRect.swift

override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    var visibleLayoutAttributes: [UICollectionViewLayoutAttributes] = [] 
    for attributes in layoutAttributesForItems.values {
        if attributes.frame.intersects(rect) {
          	visibleLayoutAttributes.append(attributes)
        }
     }
	return visibleLayoutAttributes
}