UICollectionView is showing but the cells are not showing in swift - ios

Question

I created a collectionView programmatically (without storyboard). I set the background color to red, and it is showing properly. But the cells are not showing. Does anyone know why the cells are not showing?
private let cellId = "cellId"
class InfoViewShow: NSObject, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {
private let cellHeight:CGFloat = 80
var collectionView: UICollectionView?
let layout = UICollectionViewFlowLayout()
override init() {
super.init()
setupCollectionview()
collectionView?.registerClass(InfoCell.self, forCellWithReuseIdentifier: cellId)
}
private func setupCollectionview() {
if let view = UIApplication.sharedApplication().keyWindow {
//let y = (view.frame.width * 10 / 16) + 34 + 26
collectionView = UICollectionView(frame: .zero , collectionViewLayout: layout)
collectionView?.backgroundColor = UIColor.redColor()
collectionView?.delegate = self
collectionView?.dataSource = self
collectionView?.frame = CGRectMake(0, 0, view.frame.width, view.frame.height) // y to y
}
}
func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 3
}
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCellWithReuseIdentifier(cellId, forIndexPath: indexPath)
cell.backgroundColor = UIColor.blackColor()
return cell
}
func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
return CGSizeMake(collectionView.frame.width, cellHeight)
}
func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets {
return UIEdgeInsetsMake(5, 5, 5, 5); //top,left,bottom,right
}
}

Answer 1

I dont' see you add collectionView to view.
if let view = UIApplication.sharedApplication().keyWindow {
//let y = (view.frame.width * 10 / 16) + 34 + 26
collectionView = UICollectionView(frame: .zero , collectionViewLayout: layout)
collectionView?.backgroundColor = UIColor.redColor()
collectionView?.delegate = self
collectionView?.dataSource = self
collectionView?.frame = CGRectMake(0, 0, view.frame.width, view.frame.height) // y to y
///try add
self.view.addSubview(collectionView)
}

Answer 2

You must implement numberOfSectionsInCollectionView of UICollectionViewDataSource delegate method.
This method is optional but you must implement it and return at least one section.

Answer 3

I know I am 6 years late to answer this question but I also struggled with it for 2 days before finding the mistake I was making. Hope this answer helps someone.
Check whether you have written the following two lines in your override func viewDidLoad()
collectionView.delegate = self
collectionView.dataSource = self
self.collectionView.reloadData()