确保在应用程序委托中有这个函数。

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:    (NSDictionary *)launchOptions {
   return YES;
}

确保didFinishLaunchingWithOptions返回YES。如果你碰巧删除了'return YES'行，这将导致错误。这个错误在故事板用户中可能特别常见。

你试过设置委托吗?

self.rootController.delegate = self;

在applicationDidFinishLaunchingWithOptions吗?这对我很有效，尽管我不确定为什么。

这个Swift 2解决方案对我来说很有效:

在AppDelegate -> didFinishLaunchingWithOptions中插入下面的代码

self.window!.rootViewController = storyboard.instantiateViewControllerWithIdentifier("YourRootViewController") as? YourRootViewControllerClass

我最近在用ios5 sdk构建一个项目时遇到了同样的问题。 起初，它是构建和运行正常的，但在那之后，错误出现了。 对我来说，解决办法相当简单。 所缺少的是，我的应用程序目标的摘要选项卡中的主界面属性被擦除了。所以我需要重新设置。

如果这不是重点，如果tabBarController仍然是nil，你总是可以通过编程方式创建你的窗口和根控制器。 作为备用方案，我将以下代码添加到我的项目中

- (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;
}

只有当sho的解决方案也被实现时，这才会起作用。

我也有这个错误，但没有答案已经列出是解决我的问题。 在我的例子中，日志显示是因为我在另一个子线程中分配了应用程序根视图控制器。

-(BOOL) application:(UIApplication*) application didFinishLaunchingWithOptions:(NSDictionary*) launchOptions
{
    ...
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(queue, ^{
        ...
        dispatch_async(dispatch_get_main_queue(), ^{
            ...
            [self updateTabBarTitles];
            self.window.rootViewController = self.tabBarController;
            ...
        });
    });

    [self.window makeKeyAndVisible];
    return YES;
}

通过将rootViewController分配移动到函数的末尾—就在调用makeKeyAndVisible之前:—将导致日志消息不再显示。

{
    ...
    self.window.rootViewController = self.tabBarController;
    [self.window makeKeyAndVisible];
    return YES;
}

我希望这能有所帮助。

OrdoDei给出了一个正确而有价值的答案。我添加这个答案只是为了给出一个didFinishLaunchingWithOptions方法的例子，该方法使用了他的答案以及其他关于导航控制器的评论。

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    // Override point for customization after application launch.

    // Instantiate the main menu view controller (UITableView with menu items).
    // Pass that view controller to the nav controller as the root of the nav stack.
    // This nav stack drives our *entire* app.
    UIViewController *viewController = [[XMMainMenuTableViewController alloc] init];
    self.navigationController = [[UINavigationController alloc] initWithRootViewController:viewController];

    // Instantiate the app's window. Then get the nav controller's view into that window, and onto the screen.
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // [self.window addSubview:self.navigationController.view];
    // The disabled line above was replaced by line below. Fixed Apple's complaint in log: Application windows are expected to have a root view controller at the end of application launch
    [self.window setRootViewController:self.navigationController];
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}