Getting data before navigating to a page - ios

Question

I am trying to load some data from API and then navigate to some page.
The issue is that it navigates to the page before it finishes loading the data.
I need the data to be loaded and then move to the page
What I am doing is:
func getData(){
var serviceCenter : ServiceCenter?
var serviceCenterid : Int?
print("AM HERE")
let link: String = ""
guard let Requesturl = URL(string: link) else {
print("Error: cannot create URL")
return
}
let urlRequest = URLRequest(url: Requesturl)
let config = URLSessionConfiguration.default
let session = URLSession(configuration: config)
let task = session.dataTask(with: urlRequest) {
(data, response, error) in
guard error == nil else {
print("error calling GET on /public/api/services")
print(error!)
return
}
guard let responseData = data else {
print("Error: did not receive data")
return
}
print(responseData)
guard let aViewController = UIStoryboard(storyboard: .mainStoryboard).instantiateViewController(withIdentifier: String(describing: aViewController.self)) as? aViewController else {
return
}
aViewController.selectedServiceCenterID = serviceCenterID
let navController = UINavigationController(rootViewController: aViewController)
let controllerview = AppDelegate.topViewController()
controllerview?.present(navController, animated: true, completion: nil)
do {
guard let receivedData = try JSONSerialization.jsonObject(with: responseData,options: []) as? [String: Any] else {
print("Could not get JSON from responseData as dictionary")
return
}
print(responseData)
guard let data = receivedData["data"] as? [String: Any] else {
print("Could not get status from JSON")
return
}
guard let id = data["serviceCenterId"] as? Int else {
print(error)
return
}
serviceCenterid = id
print(serviceCenterid)
} catch {
print("error parsing response from POST on /public/api/login_customer")
return
}
}
task.resume()
}
What I want to print in my ViewController :--
override func viewDidLoad() {
super.viewDidLoad()
print("DEEPLINK")
print(selectedServiceCenter)
.....
}
what I am getting is:
> AM HERE
> 10041 bytes
> before
> nil
> 10041 bytes
> 26349 --> servicecenterid
my problem is that selectedservicecenter is empty because it navigates before data is loaded! How to make the data to be loaded first and then navigate after everything is completed above?

Answer 1

In your method, the data fetch is asynchronous . As you placed the code to navigate after the task.resume(), which means after the data fetch call is initiated, the next line that gets executed is your navigation code.
What you need to do is, you need to place the navigation code inside the response block, after you print(responseData) inside the do-catch block.
Note: Make sure you execute the navigation code on main thread.

Answer 2

Write function with callback handler and in call back navigate to desired viewController this will solve your problem.