Swift: Asynchronous call in a for loop - ios

Question

I am trying to do the following in swift - Trying to reverse decode a list of addresses in an array and print their latitude/longitude coordinates. The code I have is as follows.
let addressArray = ["Address 1", "Address 2"]
var coordinatesArray = [CLLocationCoordinate2D]()
override func viewDidLoad() {
super.viewDidLoad()
createAddressList()
printAddressList()
}
func printAddressList() {
for i in 0 ..< addressArray.count {
print("Address = \(addressArray[i]) Coordinates = \(coordinatesArray[i].latitude),\(coordinatesArray[i].latitude)")
}
func createAddressList() {
for i in 0 ..< addressArray.count {
let address = addressArray[i]
geocoder.geocodeAddressString(address, completionHandler: {(placemarks, error) -> Void in
print("Address = \(address)");
if let placemark = placemarks?.first {
let coordinate = placemark.location?.coordinate
self.coordinatesArray.append(coordinate!)
}
})
}
}
}
The code prints only the first address that's decoded and nothing happens then.
I do have a fix for this like the below one, which is to move the printAddressList call from viewDidLoad method like this
func createAddressList() {
if count < self.addressArray.count {
let address = addressArray[count]
geocoder.geocodeAddressString(address, completionHandler: {(placemarks, error) -> Void in
print("Address = \(address)");
if let placemark = placemarks?.first {
let coordinate = placemark.location?.coordinate
self.coordinatesArray.append(coordinate!)
}
print("Count = \(self.count)")
self.count += 1
self.createAddressList()
})
} else {
printAddressList()
}
}
Even though the latter solution works, I see that it's not clean, would like to know the right way to do this while making the code readable and clean.

Answer 1

How about using this structure?
let workGroup = dispatch_group_create()
for i in 0..<addressArray.count {
dispatch_group_enter(workGroup)
performGeoCoding({ successCallback :
dispatch_group_leave(workGroup)
})
}
dispatch_group_notify(workGroup, dispatch_get_main_queue()){
successCallback()
printAddressList()
}
There is very nice tutorial about dispatch_group here.

Answer 2

A bit more updated would be something like:
let dispatchGroup = DispatchGroup()
for address in addressArray {
dispatchGroup.enter()
performGeoCoding { address in
dispatchGroup.leave()
}
}
dispatchGroup.notify(queue: .main) {
completionHandler()
}