Why calling a dialog with a struct drops this exception? - ios

Question

I'm trying to redirect the output of this API Call decoded in a struct but when I try to use the data to create a dialog it gives me this weird exception. As you can see, the API returns data but only when I create the dialog I see this exception. Can you help me?
Code:
struct rspServerInfo: Codable{
let ok: Bool
let info: String
}
#IBAction func backendDetails(_ sender: Any) {
guard let url = URL(string: "http://\(hostname):\(port)/STOInfo/ServerInfo")else{
return
}
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
let body: [String: AnyHashable] = [
"username": username,
"password": password,
]
request.httpBody = try? JSONSerialization.data(withJSONObject: body, options: .fragmentsAllowed)
let task = URLSession.shared.dataTask(with: request) {data, _, error in
guard let data=data, error == nil else{
return
}
do{
let response = try JSONDecoder().decode(rspServerInfo.self, from: data)
print("SUCCESS: \(response)")
let dialogMessage = UIAlertController(title: "Backend details", message: response.info, preferredStyle: .alert)
let ok = UIAlertAction(title: "OK", style: .default, handler: { (action) -> Void in
print("Ok button tapped")
})
dialogMessage.addAction(ok)
self.present(dialogMessage, animated: true, completion: nil)
}
catch{
print(error)
let dialogMessage = UIAlertController(title: "Backend details", message: "Error retreiving.", preferredStyle: .alert)
let ok = UIAlertAction(title: "OK", style: .default, handler: { (action) -> Void in
print("Ok button tapped")
})
dialogMessage.addAction(ok)
self.present(dialogMessage, animated: true, completion: nil)
}
}
task.resume()
}

Answer 1

The error message give a big clue:
Terminating app due to uncaught exception
'NSInternalInconsistencyException', reason: 'Modifications to the
layout engine must not be performed from a background thread after it
has been accessed from the main thread.' terminating with uncaught
exception of type NSException
The URLRequest run asynchronously on a background thread, including its completion handlers. You (generally) can't do UI work outside of the main thread. To display the results you need to push the operation back onto the main thread:
DispatchQueue.main.async {
// do UI work
}