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

Question

Replace in AppDelegate

 [window addSubview:[someController view]];

to

  [self.window setRootViewController:someController];

I had this same problem. Check your main.m. The last argument should be set to the name of the class that implements the UIApplicationDelegate protocol.

retVal = UIApplicationMain(argc, argv, nil, @"AppDelegate");

I had the same error when trying to change the first view controller that was loaded in

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

At first I didn't really know where the error was coming from precisely so I narrowed it down and found out what went wrong. It turns out that I was trying to change the display of a view before it actually came on screen. The solution was hence to move this code in the viewcontroller that was giving me trouble from

- (void)viewDidLoad

to

- (void)viewDidAppear:(BOOL)animated

and the error stopped appearing. My problem specifically was caused by making a UIAlertView show.

In your case I suggest you check out the code in the tabBarController's active view controller (as it is probably a problem in that view controller). If that doesn't work, try to set the starting settings in the nib file instead of in code - or if you want to do it in code, try moving the code to the tabBarController's active viewcontroller's appropriate method.

Good luck!

I got this when starting with the "Empty Application" template and then manually adding a XIB. I solved it by setting the main Nib name as suggested by Sunny. The missing step in this scenario is removing

self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];

from

application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

As it will overwrite the instance of your window created in the Xib file. This is assuming you have created a ViewController and wired it up with your window and App Delegate in the XIB file as well.

This happened to me. Solved by editing .plist file. Specify the Main nib file base name.(Should be MainWindow.xib). Hope this will help.

I run into the same problem recently, when building a project with ios5 sdk. At first it was building and running properly, but after that the error appeared.
In my case the solution was rather simple.
What was missing, was that somehow the Main Interface property in the summary tab of my application target got erased. So I needed to set it again.

If this is not the point, and if the tabBarController is still nil, you can always programmatically create your window and root controller. As a fallback I added the following code to my project

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{ 
    if (!window && !navigationController) {
        NSLog(@"Window and navigation controller not loaded from nib. Will be created programatically.");
        self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
        UIViewController *viewController1, *viewController2;
        viewController1 = [[[FirstViewController alloc] initWithNibName:@"FirstViewController_iPhone" bundle:nil] autorelease];
        viewController2 = [[[SecondViewController alloc] initWithNibName:@"SecondViewController_iPhone" bundle:nil] autorelease];

        self.tabBarController = [[[UITabBarController alloc] init] autorelease];
        self.tabBarController.viewControllers = [NSArray arrayWithObjects:viewController1, viewController2, nil];
        self.window.rootViewController = self.tabBarController;

    }
    else {
        [window addSubview:[tabBarController view]];
    }
    [self.window makeKeyAndVisible];
    return YES;
}

This will work only if sho's solution is implemented also.