GCFixedColumnHorizontalScrollingCollectionViewFlowLayout.swift

class GCFixedColumnHorizontalScrollingCollectionViewFlowLayout: UICollectionViewFlowLayout {
  var numberOfRows: UInt = 0
  var numberOfFixedColumns: UInt = 0
  var columnWidth: UInt = 0

  init(numberOfFixedColumns: UInt, columnWidth: UInt) {
    self.numberOfFixedColumns = numberOfFixedColumns
    self.columnWidth = columnWidth
    super.init()
    self.scrollDirection = .Horizontal
  }

  required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
  }

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

  override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    let fixedIndexes = numberOfRows * numberOfFixedColumns
    var attributesArray = super.layoutAttributesForElementsInRect(rect)?.filter({ (let attributes) -> Bool in
      return attributes.indexPath.row >= Int(fixedIndexes)
    })
    for index in 0..<fixedIndexes {
      if let attributes = self.layoutAttributesForItemAtIndexPath(NSIndexPath(forRow: Int(index), inSection: 0)) {
        let frame = attributes.frame
        let column = index / numberOfRows
        attributes.zIndex = 1
        attributes.frame = CGRect(x: self.collectionView!.contentOffset.x + CGFloat(columnWidth * column), y: frame.origin.y, width: frame.width, height: frame.height)
        attributesArray?.append(attributes)
      }
    }
    return attributesArray
  }
}