Call performSegue after URLSession.shared.dataTask

Question

I want to performe a Segue after sending a post request using URLSession.shared.dataTask

ViewController:

    @IBAction func Connection(_ sender: AnyObject) {
    let loginFunc = Login()
    loginFunc.login(username: username.text!, password: password.text!) { jsonString in
        let response = jsonString
        print(response)
        if response.range(of: "failure") == nil {
            self.performSegue(withIdentifier: "home", sender: nil)
        }
    }
}

Login:

class Login {
// the completion closure signature is (String) -> ()
func login(username: String, password: String, completion: @escaping (String) -> ()) {
    var request = URLRequest(url: URL(string: "http://myurl/web/app_dev.php/login_check")!)
    request.httpMethod = "POST"
    let postString = "_username=" + username + "&_password=" + password
    request.httpBody = postString.data(using: .utf8)
    var responseString = ""
    let task = URLSession.shared.dataTask(with: request) { data, response, error in
        guard let data = data, error == nil else {                                                 // check for fundamental networking error
            print("error=\(error)")
            return
        }

        if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {           // check for http errors
            print("statusCode should be 200, but is \(httpStatus.statusCode)")
            print("response = \(response)")
        }

            responseString = String(data: data, encoding: .utf8)!
            completion(responseString)
        }
        task.resume()
    }
}

It sometimes crash with the following error :

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[UIKeyboardTaskQueue waitUntilAllTasksAreFinished] may only be called from the main thread.'

Is there a better way to do it ?

Try dispatching your `performSegue` back to the main queue. – Phillip Mills Nov 09 '16 at 14:23 — Phillip Mills, Nov 09 '16 at 14:23

Nazmul Hasan · Accepted Answer · 2016-11-09T14:32:55.107

3

Trying this way :

 if response.range(of: "failure") == nil {
            NSOperationQueue.mainQueue().addOperationWithBlock {
                 self.performSegue(withIdentifier: "home", sender: nil)
            }
        }

swift3:

if response.range(of: "failure") == nil {
           OperationQueue.main.addOperation {
                self.performSegue(withIdentifier: "home", sender: nil)
            }
}

edited Nov 09 '16 at 14:32

answered Nov 09 '16 at 14:24

Nazmul Hasan

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7
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73

It works perfectly well ! If I understood well OperationQueue is waiting for the request to be done before to perform the Sergue ? – ZeenaZeek Nov 09 '16 at 14:35
yes ! operation remains in that queue until it is explicitly canceled or finishes executing its task – Nazmul Hasan Nov 09 '16 at 14:50
1

Love your answer. Thank you. – iphaaw Apr 27 '18 at 10:25

score 2 · Answer 2 · answered Nov 09 '16 at 14:32

2

As the error says you need to call perform segue in Main Thread like this

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

answered Nov 09 '16 at 14:32

Rajat

10,977
3
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55

Call performSegue after URLSession.shared.dataTask

2 Answers2

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