Delaying the loop (countdown func) - ios

Question

I've looked at many articles, none of the answers are correct. I know that these methods work, but inside a for-loop they don't. How can I create a countdown func - where I can print an array with a one second delay in between.
let array = [9, 8, 7, 6, 5, 4, 3, 2, 1]
I tried this:
for n in array {
DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
print(n)
}
}
And it prints all the numbers after 1 second. So I tried this:
override func viewDidLoad() {
super.viewDidLoad()
let timer = Timer.scheduledTimer(timeInterval: 2, target: self, selector: (#selector(printer)), userInfo: nil, repeats: true)
}
#objc func printer() {
for n in array {
print(n)
}
}
Same result. I guess these are good methods, but something's wrong.

Answer 1

Create a counter variable and another variable for the timer
var counter = 0
var timer : Timer?
In viewDidLoad create the timer
override func viewDidLoad() {
super.viewDidLoad()
timer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(printer), userInfo: nil, repeats: true)
}
In the action method increment the counter variable and invalidate the timer if the number of items in the array is reached.
#objc func printer() {
print(array[counter])
counter += 1
if counter == array.count {
timer?.invalidate()
timer = nil
}
}
Another way is DispatchSourceTimer, it avoids the #objc runtime
var timer : DispatchSourceTimer?
let interval : DispatchTime = .now() + .seconds(1)
timer = DispatchSource.makeTimerSource(queue: DispatchQueue.global())
timer!.schedule(deadline:interval, repeating: 1)
var index = 0
timer!.setEventHandler {
// DispatchQueue.main.async {
print(array[index])
}
index += 1
if index == array.count {
timer!.cancel()
timer = nil
}
}
timer!.resume()

Answer 2

For loop runs all dispatches nearly at the same time , so all of them with the same waiting Time you can depend it like this
let array = [9, 8, 7, 6, 5, 4, 3, 2, 1]
for i in 0...array.count-1 {
DispatchQueue.main.asyncAfter(deadline: .now() + Double(i) ) {
print(array[i])
}
}

Answer 3

I made countdown this way. Don't know if it is the right way, but it works.
var timeRemaining: Int = 60
countdown()
func countdown() {
if self.timeRemaining > 0 {
DispatchQueue.main.asyncAfter(deadline: .now() + 1 ) {
self.timeRemaining -= 1
self.countdown()
}
}
}

Answer 4

Try this code
let array = [9, 8, 7, 6, 5, 4, 3, 2, 1]
DispatchQueue.global().async {
for n in array {
sleep(1)
print(n)
}
}
When you use this DispatchQueue is incorrect because it will be held by waiting and then print all