iOS Concurrency with GCD & Operations

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

Part 1: Grand Central Dispatch

09. Challenge: Download a Group of Images

Episode complete

Play next episode

Next
About this episode

Leave a rating/review

See forum comments
Cinema mode Mark complete Download course materials
Previous episode: 08. Wrap an Asynchronous Function Next episode: 10. Use a DispatchSemaphore

Get immediate access to this and 4,000+ other videos and books.

Take your career further with a Kodeco Personal Plan. With unlimited access to over 40+ books and 4,000+ professional videos in a single subscription, it's simply the best investment you can make in your development career.

Learn more Already a subscriber? Sign in.

Heads up... You’re accessing parts of this content for free, with some sections shown as unmuwnehiz text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

Heads up... You’re accessing parts of this content for free, with some sections shown as iffontepit text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

00:02In the previous exercise, you wrapped asyncAdd to add a group argument. This enabled you to add asyncAdd_Group tasks to a dispatch group, which notified you when all the tasks finished. In this challenge, you’ll wrap URLSession dataTask, then use it to download a group of images.

URLSession.shared.dataTask(with: url) { data, response, error in
  completionHandler(data, response, error)
}.resume()

group.enter()
URLSession.shared.dataTask(...

defer { group.leave() }
completionHandler(data, response, error)  // already written

dataTask_Group(with: url, group: group) { data, _, error in  // don't need response
  if error == nil, let data = data, let image = UIImage(data: data) {
    images.append(image)
  }

print("All done!")
images[0]
PlaygroundPage.current.finishExecution()