我在控制台得到以下错误:

应用程序在启动结束时应该有一个根视图控制器

下面是我的应用程序:didFinishLaunchWithOptions方法:

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

    // Set Background Color/Pattern
    self.window.backgroundColor = [UIColor blackColor];
    self.tabBarController.tabBar.backgroundColor = [UIColor clearColor];
    //self.window.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"testbg.png"]];

    // Set StatusBar Color
    [[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleBlackTranslucent];

    // Add the tab bar controller's current view as a subview of the window
    self.window.rootViewController = self.tabBarController;
    [self.window makeKeyAndVisible];
    return YES;
}

在Interface Builder中，UITabBarController的委托被连接到App委托。

有人知道怎么解决这个问题吗?