Why putting a DispatchQueue delay function inside another DispatchQueue has no effect in Swift

Question

Expected Behavior:

For i = 0, print statement called after 0 second .

For i = 1, print statement called after 1.1 seconds

For i = 2, print statement called after 2.2 seconds

Actual Behavior:

Print statement called after 0, 1, 2, 3 seconds respectively i.e. inner delay function is ignored.

So why the discrepancy?

    for i in 0...3 {

        DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(i), execute: {  

            DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(i/10), execute: {
                print("function was called")
            })      
        })
    }

Answer 1

There are a number of ways you could do this. Here are 3:

Use a timer to repeat a block every second

var i = 0
Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { timer in
    i += 1
    print("hello \(i)")
    if i == 5 {
        timer.invalidate()
    }
}

Dispatch multiple async tasks

for i in 1...5 {
    DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(i)) {
        print("hello \(i)")
    }
}

Note: This queues all of the tasks up front and could overflow a queue if there were a large number of them.

Run loop in background with sleep and switch to foreground to print

DispatchQueue.global().async {
    for i in 1...5 {
        sleep(1)
        DispatchQueue.main.async {
            print("hello \(i)")
        }
    }
}

Note: This will drift a little (not be 1 second apart) if the work in the loop takes a significant amount of time.