WKInterfaceController+Animation.swift

extension WKInterfaceController {
  
  func animateWithDuration(duration: NSTimeInterval, animations: () -> Void, completion: (() -> Void)?) {
    animateWithDuration(duration, animations: animations)
    let delay = dispatch_time(DISPATCH_TIME_NOW, Int64(duration * Double(NSEC_PER_SEC)))
    dispatch_after(delay, dispatch_get_main_queue()) {
      completion?()
    }
  }
  
}