I'm setting setting FIrst view controller which will appear on my App Startup. It should appear an UIView first time as a tutorial and, from second time, another standard view. In AppDelegate I wrote this:

#import "AppDelegate.h"
#import "TabBarController.h"
#import "TutorialController.h"

@implementation AppDelegate

TabBarController * viewControllerStandard; // standard view
TutorialController * viewControllerFirst; // tutorial view

@synthesize window;

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

    if ([@"1" isEqualToString:[[NSUserDefaults standardUserDefaults] objectForKey:@"Startup"]]) {

        window.rootViewController = viewControllerStandard;

    } else { window.rootViewController = viewControllerFirst; }

    [window makeKeyAndVisible];

    return YES;
}

It doesn't return any alert but, launching app, after splashscreen, it appear only a black screen. Without that codes everything works fine. What could be wrong? Thank you!