 private let C4AnimationCompletedEvent = "C4AnimationCompleted"
 private let C4AnimationCancelledEvent = "C4AnimationCancelled"
 
-
 public class C4Animation {
     public enum Curve {
         case Linear

            NSNotificationCenter.defaultCenter().postNotificationName(C4AnimationCompletedEvent, object: self)
        }
    }
    
    
    public func addCancelObserver(action: () -> Void) -> AnyObject {
        let nc = NSNotificationCenter.defaultCenter()
        let observer = nc.addObserverForName(C4AnimationCancelledEvent, object: self, queue: NSOperationQueue.currentQueue(), usingBlock: { notification in

        case EaseIn
        case EaseInOut
    }
    /**
    The duration of the animation, measured in seconds.
    */
    public var duration: NSTimeInterval = 1

    /**
    The animation curve that the receiver will apply to the changes it is supposed to animate.
    */
    public var curve: Curve = .Linear
    
    private var completionObservers: [AnyObject] = []
