Fatal error when trying to pass data to another view controller - ios

Question

In order to practice my networking, I built an app with a text field where you can input something. I use the wikipedia API to fetch the definition of that term / name/ expression. My goal is to then display that definition into another view controller.
A button performs the segue to the new view controller, where a label displays that definition.
The get request works, but when tapping the button, I get a fatalError : "Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value".
I would like to add that the error is displayed in the "prepare for segue" function.
Here is the code for my first view controller
import UIKit
import Alamofire
import SwiftyJSON
class ViewController: UIViewController {
#IBOutlet weak var textEntryLabel: UITextField!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
//MARK: - Relevant variables
let wikipediaURl = "https://en.wikipedia.org/w/api.php"
var termDefinitionInfo: String = ""
let segueName: String = "toDefinition"
#IBAction func buttonToDefinition(_ sender: UIButton) {
// on fait la requete ici
httpCall(termDefinition: textEntryLabel.text ?? "nothing to pass")
performSegue(withIdentifier: segueName , sender: self)
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == segueName {
let secondVC = segue.destination as! DefinitionViewController
secondVC.definitionLabel.text = termDefinitionInfo
}
}
//MARK: - NETWORKING
func httpCall(termDefinition: String) {
let parameters : [String:String] = [
"format" : "json",
"action" : "query",
"prop" : "extracts",
"exintro" : "",
"explaintext" : "",
"titles" : termDefinition,
"indexpageids" : "",
"redirects" : "1",
]
//
request(wikipediaURl, method: .get, parameters: parameters).responseJSON { (response) in
if response.result.isSuccess {
//1. on affiche le tableau json initial
let definitionJSON: JSON = JSON(response.result.value)
print(definitionJSON)
// deux valeurs : pageID et definition
let pageId = definitionJSON["query"]["pageids"][0].stringValue
let pageDefinition = definitionJSON["query"]["pages"][pageId]["extract"].stringValue
self.termDefinitionInfo = pageDefinition
print(self.termDefinitionInfo)
} else {
print("Error! Could not fetch data!")
}
}
}
}
Here is the code for the second view controller
import SwiftyJSON
import Alamofire
class DefinitionViewController: UIViewController {
#IBOutlet weak var definitionLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
}```

Answer 1

Tip: Try to avoid force down casting
In your case you are trying to assign a value to an IBOutlet when it's not wired to its parent view controller. You better do this:
class DefinitionViewController: UIViewController {
#IBOutlet weak var definitionLabel: UILabel!
var labelValue: String?
override func viewDidLoad() {
super.viewDidLoad()
definitionLabel.text = labelValue
}
}
And in your first view:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == segueName {
if let secondVC = segue.destination as? DefinitionViewController {
secondVC.labelValue = termDefinitionInfo
}
}
}