cellForItemAtIndexPath never called - ios

Question

I have a UICollectionView that I added to my UIViewController in my Storyboard.
It contains a UICollectionViewCell of class BookCell and reusable identifier BookCell.
bookArray gets passed in the prepareForSegue method from the previous ViewController
cellForItemAtIndexPath never gets called. I have attempted to declare BookCollectionVC as delegate and dataSource both in Storyboard and in viewDidLoad, as you can see commented out, but that does not change anything.
I have read multiple SO answers pertaining to cell size, to the number of items in the section, to the multiple ways of declaring delegate and dataSource and have tried/double checked all of them.
Any ideas?
class BookCollectionVC: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
#IBOutlet weak var collection: UICollectionView!
var bookArray = [String]()
override func viewDidLoad() {
super.viewDidLoad()
// collection.delegate = self
// collection.dataSource = self
}
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
if let cell = collectionView.dequeueReusableCellWithReuseIdentifier("BookCell", forIndexPath: indexPath) as? BookCell {
// This never gets called
let bookIsbn = bookArray[indexPath.row]
cell.configureCell(bookIsbn)
return cell
} else {
return UICollectionViewCell()
}
}
func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
print(bookArray.count)
return bookArray.count
}
func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
return 1
}
func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
let screenSize: CGRect = UIScreen.mainScreen().bounds
let screenWidth = screenSize.width
let cellWidth = screenWidth / 4
return CGSizeMake(cellWidth,cellWidth)
}

Answer 1

As a test, don't use an if-let. Just get the cell value and print it. What is its type? Have you properly assigned the cells to be the custom class (BookCell) in your StoryBoard?