Let's take a look at how we can improve our applications to load images asynchronously while still being able to scroll a list view. This is a common issue that iOS developers run into and I'll show you how to cache images and then check to see if the request finished on the correct cell.

!codebreak <div class='filename'>VideoCell.swift</div> !codebreak !syntax-highlight let thumbnailImageView: CustomImageView = { let imageView = CustomImageView() imageView.image = UIImage(named: "taylor_swift_blank_space") imageView.contentMode = .ScaleAspectFill imageView.clipsToBounds = true return imageView }() let userProfileImageView: CustomImageView = { let imageView = CustomImageView() imageView.image = UIImage(named: "taylor_swift_profile") imageView.layer.cornerRadius = 22 imageView.layer.masksToBounds = true imageView.contentMode = .ScaleAspectFill return imageView }() !codebreak <div class='filename'>CustomImageView.swift</div> !codebreak !syntax-highlight let imageCache = NSCache() class CustomImageView: UIImageView { var imageUrlString: String? func loadImageUsingUrlString(urlString: String) { imageUrlString = urlString let url = NSURL(string: urlString) image = nil if let imageFromCache = imageCache.objectForKey(urlString) as? UIImage { self.image = imageFromCache return } NSURLSession.sharedSession().dataTaskWithURL(url!, completionHandler: { (data, respones, error) in if error != nil { print(error) return } dispatch_async(dispatch_get_main_queue(), { let imageToCache = UIImage(data: data!) if self.imageUrlString == urlString { self.image = imageToCache } imageCache.setObject(imageToCache!, forKey: urlString) }) }).resume() } }