Performing an automatic segue - ios

Question

I'm downloading remote JSON data and want my loading screen to stay up until the download is complete. Once my parse method finishes running, a segue should be called to move to the next view automatically.
I've verified that my data is properly downloading and parsing. My performSegue function is even being called when I throw up a breakpoint. But the application is still not moving to the next view.
Here's where I'm calling my parse method and then immediately calling the desired segue:
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
downloadSources(atURL: "https://newsapi.org/v1/sources?language=en")
performSegue(withIdentifier: "loadingFinished", sender: self)
}
For reference, if you need it, here is my parse method in its entirety:
func downloadSources(atURL urlString: String) {
let config = URLSessionConfiguration.default
let session = URLSession(configuration: config)
if let validURL = URL(string: urlString) {
var request = URLRequest(url: validURL)
request.setValue("49fcb8e0fa604e7aa461ee4f22124177", forHTTPHeaderField: "X-Api-Key")
request.httpMethod = "GET"
let task = session.dataTask(with: request) { (data, response, error) in
if error != nil {
assertionFailure()
return
}
guard let response = response as? HTTPURLResponse,
response.statusCode == 200,
let data = data
else {
assertionFailure()
return
}
do {
if let json = try JSONSerialization.jsonObject(with: data, options: .mutableContainers) as? [String: Any] {
guard let sources = json["sources"] as? [[String: Any]]
else {
assertionFailure()
return
}
for source in sources {
guard let id = source["id"] as? String,
let name = source["name"] as? String,
let description = source["description"] as? String
else {
assertionFailure()
return
}
self.sources.append(Source(id: id, name: name, description: description))
}
}
}
catch {
print(error.localizedDescription)
assertionFailure()
}
}
task.resume()
}
}
Thanks in advance.

Answer 1

Sounds like a closure callback is what you want.
typealias CompletionHandler = ((_ success:Bool) -> Void)?
override func viewDidLoad() {
super.viewDidLoad()
downloadSources(atURL: "www.example.com", completion: {
if success {
performSegue(withIdentifier: "loadingFinished", sender: self)
return
}
// otherwise deal with failure
})
}
func downloadSources(atURL urlString: String, completion: CompletionHandler) {
if error != nil {
completion?(false)
return
}
// finish downlaod
completion?(true)
}