ios - Display a particular viewcontroller in Xcode/swift using if else conditional statements

Question

I want a to have a conditional if statement to be run immediately when the app is open. Basically, it will be

if x = true {
  //segue to viewcontroller1
} else {
  //stay on this page
}

This will be in Xcode and coded in swift (obviously the syntax is wrong)... what is the appropriate way to write the syntax to segue to a particular view controller if the condition is true and stay on the one that normally is opened up to upon opening the app? Also, where do I put this? I considered the viewdidload method in the, normally, first displayed viewcontroller, but the variable needs to be checked before the view loads, such that the view changes to a different one if the condition is true and that one opens first instead?

Edit: I tried to set the code in the AppDelegate.swift as follows:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        if x{
            let mainStoryBoard = UIStoryboard(name: "Main", bundle: nil)
            let ViewController = mainStoryBoard.instantiateViewController(withIdentifier: "ViewController") as! ViewController
            let appDelegate = UIApplication.shared.delegate as! AppDelegate
            appDelegate.window?.rootViewController = ViewController
        } else{
          //same code as above but to different VC
        }
        return true
    }

But when I run this I get an error in the appDelegate saying that "libc++abi.dylib: terminating with uncaught exception of type NSException". What is the right way to modify this code?

Answer 1

1. If you want to select the scene before presenting. You can add the following in appDelegate.swift, in application(application: UIApplication, didFinishLaunchingWithOptions):

   var id = x ? "id1" : "id2"
   
   self.window = UIWindow(frame: UIScreen.main.bounds)
   let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
   let exampleVC: UIViewController = mainStoryboard.instantiateViewController(withIdentifier: id) as UIViewController
   self.window?.rootViewController = exampleVC
   self.window?.makeKeyAndVisible()
   

   Make sure you name the scenes in storyboard

2. If you OK with the first scene showing and then choosing to segue:

   if x {
     self.performSegue(withIdentifier: "id1", sender: self)       
   } else {
     self.performSegue(withIdentifier: "id2", sender: self)
   }
   

   Again, make sure to name the segues in storyboard

3. Another option, use UINavigationController. Set a Navigation Controller as your root view controller

   let id = x ? "id1" : "id2"
   
   let mainStoryboard = UIStoryboard(name: "MainStoryboard", bundle: nil)
   let exampleVC = mainStoryboard.instantiateViewController(withIdentifier: id) as UIViewController
   let navigationController = UINavigationController(rootViewController: exampleVC)
   self.window = UIWindow(frame: UIScreen.main.bounds)
   self.window!.rootViewController = navigationController
   self.window!.makeKeyAndVisible()