How to check if two asynchronous tasks are done with success

Question

What is the best and easiest way to implement this flowchart in a function? Right now I'm using two dispatch groups but I need to check if they're both done, and not only when they finish.

If they are done then:

• friends array will have elements
• nicknames array will have elements

note: FB is Facebook and FIR is Firebase database

Answer 1

You could do this using DispatchGroup. Try the following playground;

import UIKit
import XCPlayground

let dispatchGroup = DispatchGroup.init()

for index in 0...4 {
    dispatchGroup.enter()
    let random = drand48()
    let deadline = DispatchTime.now() + random/1000
    print("entered \(index)")
    DispatchQueue.global(qos: .background).asyncAfter(deadline: deadline, execute: {
        print("leaving \(index)")
        dispatchGroup.leave()
    })
}

dispatchGroup.notify(queue: .global()) {
    print("finished all")
}

which should output something similar to

entered 0
leaving 0
entered 1
entered 2
leaving 1
leaving 2
entered 3
leaving 3
entered 4
leaving 4
finished all