Мой код работал нормально и правильно анимировался в корневом контроллере представления. Но когда я переместил его в другой VC и перешел туда с помощью presentViewController, изображения появлялись статически и не анимировались.
Контроллер корневого представления
       @IBAction func glassFillingButtonClicked(sender: UIButton) {
    let storyBoard = UIStoryboard(name: "Main", bundle:nil)
    let nextViewController = storyBoard.instantiateViewControllerWithIdentifier("waterFilling") as! GlassFillingViewController
    self.presentViewController(nextViewController, animated:true, completion:nil)
водаНаливВК
    class GlassFillingViewController: UIViewController {
@IBOutlet weak var dropView: UIView!
@IBOutlet weak var dropImage: UIImageView!
@IBOutlet weak var dropImage2: UIImageView!
@IBOutlet weak var dropImage3: UIImageView!
@IBOutlet weak var dropImage4: UIImageView!
@IBOutlet weak var dropImage5: UIImageView!
@IBOutlet weak var dropImage6: UIImageView!
override func viewDidLoad() {
    super.viewDidLoad()
    dropAnimation()
    // Do any additional setup after loading the view, typically from a nib.
}
override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}
func addWaterDroppingAnimation(beginTime: CFTimeInterval) -> CAKeyframeAnimation {
    let waterDroppingAnimation = CAKeyframeAnimation.init(keyPath: "opacity")
    waterDroppingAnimation.beginTime = beginTime
    waterDroppingAnimation.duration = 1.0
    waterDroppingAnimation.values = [0.2,1,0.2]
    waterDroppingAnimation.repeatCount = HUGE
    return waterDroppingAnimation
}
func dropAnimation() {
    dropImage.layer.addAnimation(addWaterDroppingAnimation(0.0), forKey: "basic")
    dropImage2.layer.addAnimation(addWaterDroppingAnimation(0.2), forKey: "basic")
    dropImage3.layer.addAnimation(addWaterDroppingAnimation(0.4), forKey: "basic")
    dropImage4.layer.addAnimation(addWaterDroppingAnimation(0.6), forKey: "basic")
    dropImage5.layer.addAnimation(addWaterDroppingAnimation(0.8), forKey: "basic")
    dropImage6.layer.addAnimation(addWaterDroppingAnimation(1.0), forKey: "basic")
}
}
 
                                                                     
                                                                    