collectionViewCell未显示 - 未调用cellForItemAtIndexPath（以编程方式）

Question

我正在制作日历（刚开始）。我决定尝试以编程方式完成它，但由于一些奇怪的原因，我能够显示collectionView backgroundColor但是当我添加单元格时，它们没有显示。在我看来，一切都正确设置。在图片中，白色背景是collectionView，红色背景是包含它的视图。黄色细胞虽然没有显示出来。

我的WeekView班级

class WeekView: UIView, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

lazy var collectionView:UICollectionView = {
    let layout = UICollectionViewLayout()
    let cv = UICollectionView(frame: .zero, collectionViewLayout: layout)
    cv.delegate = self
    cv.dataSource = self
    cv.directionalLockEnabled          = true
    cv.showsVerticalScrollIndicator    = false
    cv.showsHorizontalScrollIndicator  = false
    cv.translatesAutoresizingMaskIntoConstraints = false
    cv.backgroundColor = UIColor.whiteColor()
    return cv
}()

override init(frame: CGRect) {
    super.init(frame: frame)
    backgroundColor = UIColor.redColor()
    collectionView.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: "myCell")
    setup()
}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}

func setup(){

    addSubview(collectionView)
    collectionView.leftAnchor.constraintEqualToAnchor(self.leftAnchor, constant: 50).active = true
    collectionView.topAnchor.constraintEqualToAnchor(self.topAnchor, constant: 50).active = true
    collectionView.rightAnchor.constraintEqualToAnchor(self.rightAnchor).active = true
    collectionView.heightAnchor.constraintEqualToAnchor(self.heightAnchor).active = true

}

func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 150
}

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCellWithReuseIdentifier("myCell", forIndexPath: indexPath)
    cell.backgroundColor = UIColor.yellowColor()

    return cell
}

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
    return CGSizeMake(50, 50)
}

}

我的ViewController班级

 class ViewController: UIViewController {

 override func viewDidLoad() {
    super.viewDidLoad()

setUpLeftMenuView()
    setupCalendar()
}

var menuBar:SideMenuView = {
    let menuBar = SideMenuView()
    return menuBar
}()

func setUpLeftMenuView(){

    self.view.addSubview(menuBar)
    menuBar.leftAnchor.constraintEqualToAnchor(view.leftAnchor).active = true
    menuBar.topAnchor.constraintEqualToAnchor(topLayoutGuide.bottomAnchor).active = true
    menuBar.widthAnchor.constraintEqualToConstant(100).active = true
    menuBar.heightAnchor.constraintEqualToAnchor(view.heightAnchor).active = true
}

var calendarView:WeekView = {
   let cv = WeekView()
    cv.translatesAutoresizingMaskIntoConstraints = false
    return cv
}()

func setupCalendar() {

    view.addSubview(calendarView)
    calendarView.leftAnchor.constraintEqualToAnchor(menuBar.rightAnchor).active = true
    calendarView.topAnchor.constraintEqualToAnchor(topLayoutGuide.bottomAnchor).active = true
    calendarView.rightAnchor.constraintEqualToAnchor(view.rightAnchor).active = true
    calendarView.heightAnchor.constraintEqualToAnchor(view.heightAnchor).active = true
}
}