how to manage a several asynchronous task before doing some action? - ios

Question

I am beginner in programming. I actually have my own answer of this questions and the app worked as I am expected, but I am not sure if this is the correct way to to this.
This check out action will be triggered after the user click chechoutButton. but before before this chechoutButton.isEnabled , I have to make sure 3 parameters are available (not nil). before doing this check out action, I need 3 parameters :
get user's coordinate from GPS.
get user's location address from Google Place
API
Get current date time from server for verification.
method to get user location address from Google Place API will be triggered only if I get the coordinate from GPS, and as we know, fetching data from the internet (to take date and time) also takes time, it should be done asynchronously.
how do I manage this checkoutButton only enabled if those 3 parameters are not nil ? Is there a better way according to apple guideline to do this
the simplified code are below
class CheckoutTVC: UITableViewController {
#IBOutlet weak var checkOutButton: DesignableButton!
var checkinAndCheckoutData : [String:Any]? // from MainMenuVC
var dateTimeNowFromServer : String?
var userLocationAddress : String?
let locationManager = LocationManager()
var coordinateUser : Coordinate? {
didSet {
getLocationAddress()
}
}
override func viewDidLoad() {
super.viewDidLoad()
// initial state
checkOutButton.alpha = 0.4
checkOutButton.isEnabled = false
getDateTimeFromServer()
getCoordinate()
}
#IBAction func CheckoutButtonDidPressed(_ sender: Any) {
}
}
extension CheckoutTVC {
func getDateTimeFromServer() {
activityIndicator.startAnimating()
NetworkingService.getDateTimeFromServer { (result) in
switch result {
case .failure(let error) :
self.activityIndicator.stopAnimating()
// show alert
case .success(let timeFromServer) :
let stringDateTimeServer = timeFromServer as! String
self.dateTimeNowFromServer = stringDateTimeServer
self.activityIndicator.stopAnimating()
}
}
}
func getCoordinate() {
locationManager.getPermission()
locationManager.didGetLocation = { [weak self] userCoordinate in
self?.coordinateUser = userCoordinate
self?.activateCheckOutButton()
}
}
func getLocationAddress() {
guard let coordinateTheUser = coordinateUser else {return}
let latlng = "\(coordinateTheUser.latitude),\(coordinateTheUser.longitude)"
let request = URLRequest(url: url!)
Alamofire.request(request).responseJSON { (response) in
switch response.result {
case .failure(let error) :// show alert
case .success(let value) :
let json = JSON(value)
let locationOfUser = json["results"][0]["formatted_address"].string
self.userLocationAddress = locationOfUser
self.locationAddressLabel.text = locationOfUser
self.activateNextStepButton()
}
}
}
func activateCheckoutButton() {
if dateTimeNowFromServer != nil && userLocationAddress != nil {
checkOutButton.alpha = 1
checkOutButton.isEnabled = true
}
}
}
I manage this by using this method, but I don't know if this is the correct way or not
func activateCheckoutButton() {
if dateTimeNowFromServer != nil && userLocationAddress != nil {
checkOutButton.alpha = 1
checkOutButton.isEnabled = true
}
}

Answer 1

You can use DispatchGroup to know when all of your asynchronous calls are complete.
func notifyMeAfter3Calls() {
let dispatch = DispatchGroup()
dispatch.enter()
API.call1() { (data1)
API.call2(data1) { (data2)
//DO SOMETHING WITH RESPONSE
dispatch.leave()
}
}
dispatch.enter()
API.call3() { (data)
//DO SOMETHING WITH RESPONSE
dispatch.leave()
}
dispatch.notify(queue: DispatchQueue.main) {
finished?(dispatchSuccess)
}
}
You must have an equal amount of enter() and leave() calls. Once all of the leave() calls are made, the code in DispatchGroupd.notify will be called.