Strechy UICollectionView section header

StretchCollectionViewFlowLayout.swift

//
//  StretchCollectionViewFlowLayout.swift
//
//  Created by Andrew C on 5/8/15.
//

import UIKit

class StretchCollectionViewFlowLayout: UICollectionViewFlowLayout {

    override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
        return true
    }

    override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? {
        let insets = collectionView?.contentInset
        let offset = collectionView?.contentOffset
        let minY = -insets!.top
        let attributes = super.layoutAttributesForElementsInRect(rect)

        if offset!.y < minY {
            let size = headerReferenceSize
            let deltaY = CGFloat(fabsf(Float(offset!.y - minY)))
            for attr in attributes as! [UICollectionViewLayoutAttributes] {
                if attr.representedElementKind != nil && attr.representedElementKind == UICollectionElementKindSectionHeader {
                    var rect = attr.frame
                    rect.size.height = max(minY, size.height + deltaY)
                    rect.origin.y = rect.origin.y - deltaY
                    attr.frame = rect
                    break
                }
            }
        }

        return attributes
    }
}