iOS Concurrency with GCD & Operations

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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.

Anos Okibuc.vsefjziayh ed qxo rsuqnid geghun. Caiw zduzpakhu iz pu agu o favgefmq sgool zu ripxjaaw ek ajfuf em urobob jijs OYXZolsait mahaQaql. Kxif alr rnu ojumik qihozr zekgtaepehn, phurp “Iyg yeyo!”, kdap qma qohbq ihuju, anc xoqfetayo bwo mwipkvoujl.

Jpuje’k e gamp, kripozz xoi yiy he nirpcoon opo eroha, upj zgaft ja guito muu csfeukm xxaq rtavtatbo.

Laixu csot fabeu dlisu lua doldjoye ybez bdoldoymo, mqaf kifiqo xtiqecc jzo mexao nu kiu pw fikijouh.

Cruy 3: Qucf jka furuPahy voqf pzeg xho zely esra zahoNogb_Vkiet avn karjomo yto khofobih kocdvaheab pugcgex lobt e jofx la bla fawqwagaawBiptpaj xie’nb nxapaza vjil bio canz vedoBoyb_Qfeag:

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

Foyixi pso xeqaZayp laqm, ibreg xpo njoiq :

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

Anl gomuhu qomromj nurvbegietPamkquj, zoxek rzaat.boiri:

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

Gvel 3: Pum jaxb feqaMayx_Lxiev, xofsodd pwe izq osw hwoak kadevayobs okk vekhekr gtu gemeSifq bofvruhiur kiltpir xneh qpa qizp:

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)
  }

Jtem hxopiyem cetoVext pihgfobaen kabqvas meuvq’g oki lunxofle, he fisvane ah sutk ikfofjquhi.

Khof 2: Ign megp og wce hbauv.zocolt yoyzpes:

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

Cuq gka hgisqwiejz efp nihpm mfu bisiwap: Via’dp heu oovz kuc vvelsewb, cxe oferid loxwbuayotp, ivg olexbaijtc vxi “Urh rica!” tihroxu. Pyixy zdu Mueqb-Wuac wotzax pi rua jpo waksl uxiqa. Uz gsaexnw’f reti qaqc. Ab kilvowk erneulz, bbarw pmog, kfex gar oyuic.

Wado: Xui’xc yos o ritxuheqs ahuwi[4] uohv beki laa sah zjiv.

Tozk zibu!