Application windows are expected to have a root view controller at the end of application launch

Question

I am using the facebook iOS SDK setup tutorial: https://developers.facebook.com/docs/mobile/ios/build/

After Step 4: Adding Log Out to your App,

I get a blank white screen on the 5.1 simulator (xcode 4.3.2) and the console shows a message:

Application windows are expected to have a root view controller at the end of application launch

EDIT-1

Thanks for your responses; I chose a "Single View Application" template while creating the app. In the MainStoryBoard.storyboard, I created an object and assigned the MyGreatIOSAppAppDelegate class to it. Drag-dropped the viewController outlet of this object to the View Controller.

here is the code in MyGreatIOSAppAppDelegate.m

#import "MyGreatIOSAppAppDelegate.h"
#import "xxxViewController.h"

@implementation IJSAppDelegate

@synthesize window = _window;
@synthesize viewController = _viewController;
@synthesize facebook;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];

    // Add the logout button
    UIButton *logoutButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    logoutButton.frame = CGRectMake(40, 40, 200, 40);
    [logoutButton setTitle:@"Log Out" forState:UIControlStateNormal];
    [logoutButton addTarget:self action:@selector(logoutButtonClicked)
           forControlEvents:UIControlEventTouchUpInside];
    [self.viewController.view addSubview:logoutButton];    

    facebook = [[Facebook alloc] initWithAppId:@"id" andDelegate:self];

    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    if ([defaults objectForKey:@"FBAccessTokenKey"] 
        && [defaults objectForKey:@"FBExpirationDateKey"]) {
        facebook.accessToken = [defaults objectForKey:@"FBAccessTokenKey"];
        facebook.expirationDate = [defaults objectForKey:@"FBExpirationDateKey"];
    }
    if (![facebook isSessionValid]) {
        [facebook authorize:nil];
    }
    return YES;
}


- (BOOL)application:(UIApplication *)application openURL:(NSURL *)url
  sourceApplication:(NSString *)sourceApplication annotation:(id)annotation {
    return [facebook handleOpenURL:url]; 
}

- (void)fbDidLogin {
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    [defaults setObject:[facebook accessToken] forKey:@"FBAccessTokenKey"];
    [defaults setObject:[facebook expirationDate] forKey:@"FBExpirationDateKey"];
    [defaults synchronize];
}

// Method that gets called when the logout button is pressed
- (void) logoutButtonClicked:(id)sender {
    [facebook logout];
}

- (void) fbDidLogout {
    // Remove saved authorization information if it exists
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    if ([defaults objectForKey:@"FBAccessTokenKey"]) {
        [defaults removeObjectForKey:@"FBAccessTokenKey"];
        [defaults removeObjectForKey:@"FBExpirationDateKey"];
        [defaults synchronize];
    }
}

@end

Solution

Check that you have the following line in your application delegate's application:didFinishLaunchingWithOptions: method:

self.window.rootViewController = self.viewController;