Perform Segue in ViewDidLoad

Question

I`m trying to perform a segue if its the first time the app is loading. I can see my print message in the debugger, but the Perform Segue is not working. I don't get any errors. Can somebody please tell me whats wrong?

import UIKit
import LocalAuthentication
let isFirstLaunch = UserDefaults.isFirstLaunch()
extension UserDefaults {
    // check for is first launch - only true on first invocation after app install, false on all further invocations
    // Note: Store this value in AppDelegate if you have multiple places where you are checking for this flag
    static func isFirstLaunch() -> Bool {
        let hasBeenLaunchedBeforeFlag = "hasBeenLaunchedBeforeFlag"
        let isFirstLaunch = !UserDefaults.standard.bool(forKey: hasBeenLaunchedBeforeFlag)
        if (isFirstLaunch) {

            UserDefaults.standard.set(true, forKey: hasBeenLaunchedBeforeFlag)
            UserDefaults.standard.synchronize()
        }
        return isFirstLaunch
    }
}

class loginVC: UIViewController {





    override func viewDidLoad() {

        super.viewDidLoad()

        if  isFirstLaunch == false {
          performSegue(withIdentifier: "setPassword", sender: self)
            print("testFalse") }
            else {
            performSegue(withIdentifier: "setPassword", sender: self)
            print("testTrue")}


        //       Do any additional setup after loading the view, typically from a nib.




    }

`testTrue` for the first launch and `testFalse` for the others? — Vyacheslav, Aug 12 '17 at 19:05
is `override func prepare(for segue: UIStoryboardSegue, sender: Any?) {` fired? — Vyacheslav, Aug 12 '17 at 19:17
show where is segue defined? Did you try to move it to viewDidAppear for exapmle? — Michal Rogowski, Aug 12 '17 at 19:23
Moved it to ViewDidAppear and that fixed the problem. Thank You Salsores and Smartcat — Paal Aune, Aug 12 '17 at 20:00

score 43 · Accepted Answer · answered Aug 12 '17 at 19:22

43

You can't use performSegue() from within viewDidLoad(). Move it to viewDidAppear().

At viewDidLoad() time, the current view isn't even attached to the window yet, so it's not possible to segue yet.

answered Aug 12 '17 at 19:22

Smartcat

2,834
1
13
25

Thank you Smartcat. Moved the code to ViewDidAppear() and it works fine now! – Paal Aune Aug 12 '17 at 19:59
Is it okay to call it from viewWillAppear do you know? It's testing okay for me but I'm worried about outlier cases or low-performance devices... – paul_f Jun 24 '19 at 21:22
1

@paul_f I've successfully done so in some of my production code, but others have had trouble. See this [SO](https://stackoverflow.com/a/37493606/8441876) for example. Maybe it depends on if there's a transition animation to be used? If you spot something definitive from Apple, please post here. – Smartcat Jun 25 '19 at 17:52
@Smartcat you literally saved me a headache. Worst part is that I was really close, but I was approaching the problem in the wrong way. I was trying to run `performSegue` inside `viewWillAppear`. Just moving it to `viewDidAppear` fixed everything. – Mihail Minkov Oct 17 '19 at 14:54

score 1 · Answer 2 · answered Nov 19 '17 at 18:28

1

You can also use a different approach - change the main window's rootViewController to the view controller of your choice depending on isFirstLaunchboolean

UIApplication.shared.keyWindow?.rootViewController = setPasswordViewController

answered Nov 19 '17 at 18:28

cohen72

2,830
29
44

Perform Segue in ViewDidLoad

2 Answers2

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