How to load the desired viewController in iOS?

Question

Objective-C

When loading, I need the application to check what value is currently in UserDefaults in one key, and depending on the value, open different viewControllers. Simply put, if the user is already logged in, it opens the main screen, if not, then the authorization screen. Where and how to implement it?

Answer 1

In the case of the storyboard, I do the following:
- in the Deployment Info of the desired target, I remove the Main Interface ;
- add the following code to the application:didFinishLaunchingWithOptions: AppDelegate method

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"YourStoryboardName" bundle:nil];
   
    UIViewController *firstViewControllerToShow = nil;
    
    if (yourCondition) {
        firstViewControllerToShow =
            [storyboard instantiateInitialViewController];
    } else {
        firstViewControllerToShow =
            [storyboard instantiateViewControllerWithIdentifier:@"YourAlternativeSceneStoryboardID"];
    }
    
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.rootViewController = firstViewControllerToShow;
    [self.window makeKeyAndVisible];
    
    return YES;
}

where yourCondition is the condition depending on which one or another ViewController should be shown, for example, whether the user is registered or not. If registered, the ViewController that is specified as Initial in the storyboard will be shown. If not, a ViewController with an ID of YourAlternativeSceneStoryboardID .
Actually, without a storyboard, everything is the same, but without a storyboard. :)

Answer 2

If it's a storyboard, then my tactic is usually this:
1. Create an InitialController, assign it to initial in the storyboard.
2. In it, in viewDidLoad, I check if there is a user, if it is authorized and display the controller that I need:

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self checkAuth];
}

- (void)checkAuth
{
    UIStoryboard* storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    UIViewController *navController;
  if (![AUUser currentUser]) {
        navController = [storyboard instantiateViewControllerWithIdentifier:@"authContainer"];
    } else {
        navController = [storyboard instantiateViewControllerWithIdentifier:@"mainViewContainer"];
    }
    
    navController.view.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    navController.view.frame = self.view.bounds;
   
    [self addChildViewController:navController];
    [self.view addSubview:navController.view];
    self.currentController = navController;
}

Answer 3

Are you using a storyboard or not?