在URLSession.shared.dataTask中执行performSegueWithIdentifier（with：url）

Question

I am checking on a test Server if a user is registered. If the server gives back, that the username and password are true, i want to perform a Segue with the identifier "Login". If I put the performeSegue inside the URLSession dataTask the program crashes with this error: "terminating with uncaught exception of type NSException" I don't know what to do. because of the resume() function I can't put the performSegue outside of the dataTask. It would be executed before i get the data from the server.

Here is my Code:

@IBAction func login(_ sender: AnyObject) {
    var session:String?

    if userName.text!.isEmpty || logInPassword.text!.isEmpty{
        let noUserName = UIAlertController(title: "Kein Benutzername oder Passwort", message: "Bitte geben sie einen Benutzernamen und ein Passwort ein.", preferredStyle: .alert)
        noUserName.addAction(OKAction)
        self.present(noUserName, animated: true)
    } else {
        //Implementing URLSession
        let urlString = "http://www.***.me/playground/api/v1/user/login/\(userName.text!)/\(logInPassword.text!)"
        guard let url = URL(string: urlString) else {
            print("Error: couldn't open link")
            return
        }

        URLSession.shared.dataTask(with: url) { (data, response, error) in
            guard let responseData = data else {
                print("Error: did not receive data")
                return
            }

            //Implement JSON decoding and parsing
            do {
                //Decode retrived data with JSONDecoder and assing type of Article object
                let personsData = try JSONDecoder().decode(LoginTest.self, from: responseData)
                session = personsData.session
                dump(personsData)

            } catch let jsonError {
                print("Error: \(jsonError)")

            }

            if session != nil{
                //loging in
                print("now loged in")
                self.performSegue(withIdentifier: "Login", sender: self)
                //here it crashes

            } else {
                let alertWrongPassword = UIAlertController(title: "Benutzername und Passwort stimmen nicht überein", message: "Bitte versuchen Sie es erneut.", preferredStyle: .alert)
                alertWrongPassword.addAction(self.OKAction)
                self.present(alertWrongPassword, animated: true)
            }
        }.resume()
        //End implementing URLSession
    }
}

Answer 1

According to the exception reason you have to perform the segue on the main thread

DispatchQueue.main.async {
    self.performSegue(withIdentifier: "Login", sender: self)
}