title: How do I get NSTimer to restart updating a label when returning to a ViewController?
body: <p>I have a basic Timer app (the start of something a bit more complex) and I'm trying to allow the user to open a new view, change some settings, then return to the time screen and have the timer still ticking down. </p>
  
  <p>At the moment, when the user returns to the timer screen <code>ViewController</code>, my timer is still firing and printing the time to the console, but the label has stopped updating. </p>
  
  <p>How do I start the timer updating the label again?</p>
  
  <pre><code>class Countdown 
  {
      var initial = 100
      var count = 100
      var timer: NSTimer!
      var timerRunning = false
  }
  
  var globals = Countdown()
  
  class ViewController: UIViewController {
  
  @IBOutlet weak var timer1Label: UILabel!
  
  @IBAction func unwindSegue(sender: UIStoryboardSegue) {} // Added to get rewind segue to work as recommended by Ben Sullivan
  
  @IBAction func timer1(sender: AnyObject) 
  {
      globals.timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: #selector(ViewController.timerRunning), userInfo: nil, repeats: true)
  }
  
  override func viewDidLoad() {
      super.viewDidLoad()
      // Do any additional setup after loading the view, typically from a nib.
  }
  
  func timerRunning()
  {
      globals.timerRunning = true
      let minutes = (globals.count / 60) % 60;
      let seconds = globals.count % 60
      print("\(minutes):\(seconds)")
      globals.count = globals.count - 1
      timer1Label.text = String("\(minutes):\(seconds)")
  } 
  
  override func didReceiveMemoryWarning() {
      super.didReceiveMemoryWarning()
      // Dispose of any resources that can be recreated.
  }
  
  }
  </code></pre>
  
  <p>At the moment, the settings view controller has nothing on it - just a button that returns the user to ViewController.</p>