iOS: load main interface programmatically

AppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    UIStoryboard *mainStoryboard = nil;
    
    BOOL showLogin = NO;
    if(showLogin == NO)
    {
        // mainStoryboard method looks like:
        // return [UIStoryboard storyboardWithName:@"Main" bundle:nil];
        mainStoryboard = [UIStoryboard mainStoryboard]; 
    }
    else
    {
        mainStoryboard = [UIStoryboard loginStoryboard];
    }
    
    
    UIViewController *rootController = [mainStoryboard instantiateInitialViewController];
    NSAssert(rootController, @"no user interface, what is this? a web service??");
    self.window.rootViewController = rootController;
    [self.window makeKeyAndVisible];
    return YES;
}

AppDelegate.swift

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        self.window = UIWindow(frame: UIScreen.mainScreen().bounds)
        var mainStoryboard: UIStoryboard? = nil
        
        let showTutorial = true
        
        if(showTutorial) {
            mainStoryboard = UIStoryboard.tutorialStoryboard()
        }
        else {
            // mainStoryboard method looks like:
            // return UIStoryboard(name: "Main", bundle: nil)
            mainStoryboard = UIStoryboard.mainStoryboard()
        }
        
        let rootController = mainStoryboard!.instantiateInitialViewController()
        assert(rootController != nil, "no user interface, must be the D day")
        self.window?.rootViewController = rootController
        self.window?.makeKeyAndVisible()
        
        return true
    }

AppDelegate.m, line 3: What's the intent of creating a new window?
The app ran into some problems when I use this code snippet, comment that line, all's OK!

Sorry @kenmux, didn't see your comment till now (guess GH doesn't post notifications on comments to Gists). I was creating a window myself because I have not set any storyboard to be the Main Interface, If you don't set it, you are responsible for creating the window yourself, and since you are loading appropriate storyboard through your code anyway, setting a Main Interface didn't make any sense either.

Thank you so much for your post.

thanks for this)

Note that as of Swift 4 that UIScreen.mainScreen().bounds (line 2) has been renamed to UIScreen.main.bounds