Changing root view controller after iOS app has loaded.

Question

In order to show my login screen when the app loads, and not after the user logs in, I have decided to add an auth object in NSUserDefaults when the user logs in successfully. When the app is launched that auth parameter is checked, and the view controller is set accordingly (if the user is auth it'll show a feed, if not it'll show a login screen) In the latter case, I have the app delegate reset the root view controller to the feed after the user has logged in. Is this bad practice or is there a better way of doing this?

In the app delegate:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary     *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    IIViewDeckController* deckController = [self generateControllerStack];
    self.rightController = deckController.rightController;
    self.centerController = deckController.centerController;

    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

    if([[defaults objectForKey:@"auth"] isEqualToNumber:[NSNumber numberWithInt:1]]){
        self.window.rootViewController = deckController;
    }else{
        UIStoryboard *sb = [UIStoryboard storyboardWithName:@"MainStoryboard"
                                                 bundle:nil];
        UIViewController* vc = [sb instantiateViewControllerWithIdentifier:@"loginViewController"];
        self.window.rootViewController = vc;
    }
    [self.window makeKeyAndVisible];
    [[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleBlackOpaque animated:NO];
    return YES;
}

- (void) setRoots
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    IIViewDeckController* deckController = [self generateControllerStack];
    self.rightController = deckController.rightController;
    self.centerController = deckController.centerController;
    self.window.rootViewController = deckController;
    [self.window makeKeyAndVisible];
}

In the login view controller:

- (IBAction)loginClick:(id)sender {
    if([_emailField.text length]>0&&[_passField.text length]>0){
        NSString *user = _emailField.text;
        NSString *pass = _passField.text;
        [[API sharedInstance] login:user andPass:pass onCompletion:^(NSDictionary *json){
            NSLog(@"%@", json);
            if(![json objectForKey:@"error"]){
                [API sharedInstance].authorized = 1;
                NSNumber *auth = [NSNumber numberWithInt:1];
                NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
                [defaults setObject:auth forKey:@"auth"];
                [defaults synchronize];

                captureYouAppDelegate *app = [[UIApplication sharedApplication] delegate];
                [app setRoots]; 
            }else{
                [API sharedInstance].authorized = 0;
            }
        }];
    }else{
        if([_emailField.text length]<1){
            [_emailField becomeFirstResponder];
        }else{
            [_passField becomeFirstResponder];
        }
    }
}

I'm wondering if there is a better or easier way than doing that. Thank you!

Answer 1

Just to clarify. I had reset UIWindow's rootViewController before without any problem but when attempting to do so while allowing device rotation I ran into some issues — Rotation just stopped working.

I found the following directly from Apple's docs while trying to debug. The link below has a number of guidelines about working with UIWindow. These are all related to device rotation but still good to know.

Short answer, use a root controller and add child view controllers. You can then swap out the child VCs with no problem.

• You have added your view controller's UIView property to UIWindow as a subview.

Developers are discouraged from adding the view property of any view controller as a subview of UIWindow. Your application's root view controller should be assigned to the app window's rootViewController property either in Interface Builder, or at runtime before returning from application:didFinishLaunchingWithOptions:. If you need to display content from more than one view controller simultaneously, you should define your own container view controller and use it as the root view controller. See Creating Custom Container View Controllers.

Check this technical Q&A for more details.

Answer 2

I don't think reset the window.rootViewController is a bad practice. However, there is no need to recreate a window.
If you don't want to use the previous view controller, just replace the window's rootViewController with the new view controller. If you do want to switch back to your previous view controller, use -presentViewController: animated: completion: to present your view controller may be a better alternative.