Apple Watch — Load animated image from sprite sheet

gistfile1.swift

func loadingAnimationImage() -> UIImage? {
        let sheet = UIImage(named: "activity-large")
        var images = [UIImage]()

        if sheet == nil {
            return nil
        }

        for (var currentX = 0; currentX < Int(sheet!.size.width); currentX += 54) {
            let splitRef = CGImageCreateWithImageInRect(sheet?.CGImage, CGRect(x: CGFloat(currentX), y: 0.0, width: 54.0, height: sheet!.size.height * 2))
            images.append(UIImage(CGImage: splitRef, scale: scale, orientation: .Up)!)
        }

        let animatedImage = UIImage.animatedImageWithImages(images, duration: 0.5)
        WKInterfaceDevice.currentDevice().addCachedImage(animatedImage, name: LoadingImageIdentifier)
        return animatedImage
    }

    func generateLoadingAnimation() {
        if let _: AnyObject = WKInterfaceDevice.currentDevice().cachedImages[LoadingImageIdentifier] {
            firstImage.setImageNamed(LoadingImageIdentifier)
            firstImage.startAnimating()

            secondImage.setImageNamed(LoadingImageIdentifier)
            secondImage.startAnimating()
        } else if let image = loadingAnimationImage() {
            firstImage.setImage(image)
            firstImage.startAnimating()

            secondImage.setImage(image)
            secondImage.startAnimating()
        }
    }
    
    // Image at https://github.com/contentful-labs/ContentfulWatchKitExample/blob/master/WatchKit%20Extension/Images.xcassets/activity-large.imageset/activity-large%402x.png