Know when an iteration over array with async method is finished

Question

Lets say i have an array of strings, and i call an async method that returns an int from it. I want to know when i have those int values in my array of ints.

let rndStrings = ["a", "b", "c"]
var rndInts = [Int]()
rndStrings.forEach { rndString in 
   someAsyncMethod { intResult in
     rndInts.append(intResult)
   }
}

I want to wait until rndInts has all 3 values

I am not sure , But if you want to _Know when your array is changed_ , you can maybe use `Property Observers` , maybe , which will be called every time you make changes to your array , so that means at the initialisation as well ! — Shubham Bakshi, Oct 20 '18 at 07:45

score 4 · Answer 1 · answered Oct 20 '18 at 05:18

4

Don't wait. Get notified with DispatchGroup.

let rndStrings = ["a", "b", "c"]
let group = DispatchGroup()
var rndInts = [Int]()
rndStrings.forEach { rndString in 
   group.enter()
   someAsyncMethod { intResult in
     rndInts.append(intResult)
     group.leave()
   }
}
group.notify(queue: DispatchQueue.main) {
   print("finished")
}

answered Oct 20 '18 at 05:18

vadian

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Awesome! Theres any way to set a timeout for this group? – Godfather Oct 20 '18 at 05:22
Try [wait(timeout:)](https://developer.apple.com/documentation/dispatch/dispatchgroup/1780590-wait) instead of `notify`. – vadian Oct 20 '18 at 05:26
but this will block, isn't? – Godfather Oct 20 '18 at 05:26
Yes, it blocks the current thread. Alternatively use a separate `DispatchTimer` – vadian Oct 20 '18 at 05:37

Know when an iteration over array with async method is finished

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