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

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Challenge: Download a Group of Images

In 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)
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) {
print("All done!")