Three blinking lights (chained animated UIImageViews).

gistfile1.swift

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var light1: UIImageView!
    @IBOutlet weak var light2: UIImageView!
    @IBOutlet weak var light3: UIImageView!

    enum BlinkingStatus {
        case Blinking, Off
    }
    
    var blinkingStatus: BlinkingStatus = .Blinking

    override func viewDidLoad() {
        super.viewDidLoad()
        
        self.startBlinking()
    }
    
    func startBlinking() {
        self.blinkingStatus = .Blinking
        self.lightLight(1)
    }

    func stopBlinking() {
        self.blinkingStatus = .Off
    }
    
    func getLight(number: Int) -> UIImageView {
        switch number {
        case 1: return self.light1
        case 2: return self.light2
        case 3: return self.light3
        default: return self.light1
        }
    }

    func lightLight(number: Int) {
        var light = self.getLight(number)
        UIView.animateWithDuration(1.0,
            delay: 0.0,
            options: nil,
            animations: {
                light.alpha = 1
            },
            completion: { finished in
                self.douseLight(number)
            }
        )
    }

    func douseLight(number: Int) {
        var light = self.getLight(number)
        UIView.animateWithDuration(0.5,
            delay: 0.0,
            options: nil,
            animations: {
                light.alpha = 0
            },
            completion: { finished in
                if self.blinkingStatus == .Blinking {
                    self.lightLight((number % 3) + 1)
                }
            }
        )
    }
}