selecting alternative first view controller from story board at application startup

Question

I've just started on iOS programming and so far the tutorials and answers I found here have been a great help to move forward. However, this particular problem has been bumming me all night and I can't find an answer that "feels right".

I'm writing an application that connects to a remote service and the users need to sign in before they can use it. When they start using the application, their first view should be the sign in dialog; when they've authenticated before, they immediately see the overview page.

The project uses story boards - which I think is a great feature - so most of the code that selects and loads the root view controller is already taken care of. I thought the best place to add my logic is the application:didFinishLaunchingWithOptions: method of the AppDelegate:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:
      (NSDictionary *)launchOptions
{
    // select my root view controller here based on credentials present or not
    return YES;
}

But this brought up two questions:

1. Inside this particular delegate method, the root view controller has already been selected (and loaded?) based on the story board. Could I move to an earlier spot in the loading process to override the first view controller selection or would that needlessly complicate matters?

2. To override the first view controller I need a reference to the story board, but I couldn't find a better way than to use the storyboardWithName:bundle: constructor of UIStoryboard. That feels wrong, the application should already have a reference to the story board, but how can I access it?

Update

I worked out the second issue I was having, as I found my answer here:

UIStoryboard: What's the Correct Way to Get the Active Storyboard?

NSBundle *bundle = [NSBundle mainBundle];
NSString *sbFile = [bundle objectForInfoDictionaryKey:@"UIMainStoryboardFile"];
UIStoryboard *sb = [UIStoryboard storyboardWithName:sbFile bundle:bundle];

The above will create a new story board instance; to get the active instance, it's a whole lot simpler:

UIStoryboard *sb = [[self.window rootViewController] storyboard];

In the story board file itself you have to set an identifier for the view you wish to load, e.g. LoginDialog. Afterwards you instantiate the view like this:

LoginViewController *login = [sb instantiateViewControllerWithIdentifier:@"LoginDialog"];
[self.window setRootViewController:login];

Within another view controller, the following suffices:

UIStoryboard *sb = self.storyboard;
LoginViewController *login = [sb instantiateViewControllerWithIdentifier:@"LoginDialog"];
[self presentViewController:login animated:NO completion:nil];

Answer 1

You can just reset the root view controller of the window

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:
      (NSDictionary *)launchOptions
{
   if(your_condition) {
       UIViewController *newRoot = [your implementation];
       self.window.rootViewController = newRoot;
   }
   return YES;
}

This is worked for me, Xcode5.0.1

Answer 2

I have a similar scenario as yours. My application uses a UINavigationController as the root view controller. If the user is logged in, I want to present him/her with NotLoggedInViewController, while if it's logged in I want to show the LoggedInViewController.

In a storyboard a UINavigationController can only have one child, so you have to be able to programmatically assign another root view controller to it.

I start by creating a custom navigation controller class, let's name it MyNavigationController. In the storyboard I assign this custom class to the navigation controller object.

Still in the storyboard, I then model both view controllers, and connect one of them to the navigation controller object. Since I need to be able to access them from my code later on, I assign each of them an identifier using the XCode inspector on the right. These identifiers which can be arbitrary strings, but to things simple I just use the class names.

Finally I then implement the viewDidLoad method on MyNavigationController class:

BOOL isLoggedIn = ...;

- (void)viewDidLoad {
  id rootController;
  if (isLoggedIn) {
    rootController = [self.storyboard instantiateViewControllerWithIdentifier:@"LoggedInViewController"];
  } else {
    rootController = [self.storyboard instantiateViewControllerWithIdentifier:@"NotLoggedInViewController"];
  }
  self.viewControllers = [NSArray arrayWithObjects:rootController, nil];
}