iOS Concurrency with GCD & Operations

Sep 12 2023 · Swift 5.8, macOS 13, iOS 16, Xcode 14.3

Part 3: Operations & OperationQueues

19. Challenge: Download Images in OperationQueue

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Previous episode: 18. Asynchronous Operations Next episode: 20. Dependencies

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Challenge: Download Images in OperationQueue

The playground in the starter folder has part of the ImageLoadOperation and the same image url components you used in the dispatch group challenge in Part 1. The first part of your challenge is to fill in the operation’s main function, to download an image from the input url. The second part of your challenge is to use instances of this operation in an OperationQueue to download all the images.

open class AsyncOperation: Operation {
class ImageLoadOperation: AsyncOperation {
  private let url: URL
  var image: UIImage?

  init(url: URL) {
    self.url = url
  // TODO: Call dataTask with url and save image
  override func main() {
URLSession.shared.dataTask(with: url) { [weak self] data, response, error in
  guard let self else { return }

defer { self.state = .finished }
guard error == nil, let data else { return }
image = UIImage(data: data)
let base = ""
let ids = [466881, 466910, 466925, 466931, 466978, 467028, 467032, 467042, 467052]
var images: [UIImage] = []
let queue = OperationQueue()
for id in ids {
  guard let url = URL(string: "\(base)\(id)-jpeg.jpg") else { continue }

let op = ImageLoadOperation(url: url)
op.completionBlock = {
  if let image = op.image { images.append(image) }
3.188688039779663 (or ~1.284000039100647 or 2.58...)
w 600 h 516