Populating UIView with results of NSURL - ios

Question

I am using an API that returns JSON which is parsed into a String. I want to then use this string as a label on another view controller. I tried using completion blocks but I can't get it to work, it continuously returns "Fatal error: expected optional returned nil" but I can't figure out where. I'm assuming it has something to do with asynchronous calls not allowing the popup class to populate with the String that the API hasn't returned yet.
func summarizeArticle(finished: () -> Void) {
let formatText = (searchText.text?.replacingOccurrences(of: " ", with: "_"))!
articleNameFormatted = ("https://en.wikipedia.org/wiki/" + formatText)
let request : NSMutableURLRequest = NSMutableURLRequest()
request.url = NSURL(string: urlString + articleNameFormatted) as URL!
request.httpMethod = "POST"
let url = request.url
URLSession.shared.dataTask(with:url!) { (data, response, error) in
if error != nil {
print(error!)
} else {
do {
let parsedData = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as! [String:Any]
articleSummary = parsedData["sm_api_content"] as! String
print(articleSummary)
} catch let error as NSError {
print(error)
}
}
}.resume()
finished()
}
#IBAction func summarizeButtonPressed(_ sender: Any) {
self.view.endEditing(true)
summarizeArticle{
let popupVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "sbPopupVC") as! PopupViewController
popupVC.view.frame = self.view.frame
self.addChildViewController(popupVC)
self.view.addSubview(popupVC.view)
popupVC.didMove(toParentViewController: self)
}
}
The second view controller then uses this function which is supposed to grab the text from a global variable set by the previous functions:
override func viewDidLoad() {
super.viewDidLoad()
popupView.layer.cornerRadius = 10.0
popupView.clipsToBounds = true
summaryText.text = articleSummary
view.backgroundColor = UIColor.black.withAlphaComponent(0.0)
self.showAnimation()
}

Answer 1

Instead of making articleSummary a global variable, try this:
1) Make articleSummary local to your summarizeArticle() function.
2) In the class definition for your view controller with identifier "sbPopupVC", add an instance variable called something like articleSummaryText.
3) Get rid of the completion handler on summarizeArticle() and move all the code that was in there to the completion block of your URLSession API call.
4) In that completion block, right before self.addChildViewController(popupVC), add this line: popupVC.articleSummaryText = articleSummary
5) Finally, in viewDidLoad() of your popupVC, set summaryText.text = articleSummaryText.