iPhone 6.0模拟器: Application windows are expected to have a root view controller at the end of application launch

Question

当我在 iPhone 6.0 模拟器中运行我的应用程序时，它显示

应用程序窗口预计在应用程序启动结束时有一个 Root View Controller

在其他模拟器中它不存在。为什么？这个错误是什么意思？

我的应用程序的导航流程如下:首先我的应用程序应该显示登录屏幕。进入应用程序后，我需要使用选项卡栏显示一个 View 。在该 View 中会有很多按钮，当我们单击这些按钮时，它应该显示相应的 View Controller ，而不带选项卡栏。这就是我将这些导航 Controller 添加到窗口的原因。

这是我的 didFinishLaunchingWithOptions 代码

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.tabBarController = [[UITabBarController alloc] init];
    self.window.rootViewController = self.tabBarController;

    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.backgroundColor=[UIColor blackColor];

    [application setStatusBarStyle:UIStatusBarStyleBlackOpaque];

    Object1 = [[Class1 alloc] initWithNibName:@"Class1" bundle:nil];
    tempNav=[[UINavigationController alloc]initWithRootViewController:Object1];
    tempNav.navigationBar.hidden=YES;
    tempNav.view.frame  = CGRectMake(0.0f, 20.0f, 320.0f, 460.0f);
    self.window addSubview:tempNav.view]; 

    LoginObj = [[Login alloc] initWithNibName:@"Login" bundle:nil];
    navController=[[UINavigationController alloc]initWithRootViewController:LoginObj];
    navController.navigationBar.hidden=YES;
    navController.view.frame  = CGRectMake(0.0f, 20.0f, 320.0f, 460.0f);
    [self.window addSubview:navController.view];

    Obj2 = [[Class2 alloc] initWithNibName:@"Class2" bundle:nil];
    navController1=[[UINavigationController alloc]initWithRootViewController:Obj2];
    navController1.navigationBar.hidden=YES;
    navController1.view.frame  = CGRectMake(0.0f, 20.0f, 320.0f, 460.0f);
    [self.window addSubview:navController1.view];

    Obj3 = [[Class3 alloc] initWithNibName:@"Class3" bundle:nil];
    navController2=[[UINavigationController alloc]initWithRootViewController:Obj3];
    navController2.navigationBar.hidden=YES;
    navController2.view.frame  = CGRectMake(0.0f, 20.0f, 320.0f, 460.0f);
    [self.window addSubview:navController2.view];

    Obj4 = [[Class4 alloc] initWithNibName:@"Class4" bundle:nil];
    navController3=[[UINavigationController alloc]initWithRootViewController:Obj4];
    navController3.navigationBar.hidden=YES;
    navController3.view.frame  = CGRectMake(0.0f, 20.0f, 320.0f, 460.0f);
    [self.window addSubview:navController3.view];

    [self.window makeKeyAndVisible];

    return YES;  
}

Answer 1

正如 wattson12 所说，您需要在应用程序委托(delegate)中执行以下操作:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    self.mainViewController = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
    self.window.rootViewController = self.mainViewController;    // you need this line!
    [self.window makeKeyAndVisible];
    return YES;
}

如果您没有显式设置 UIWindow rootViewController property ，您将看到此消息。

如果您使用 Xcode 4.5 创建新项目，则模板应用程序委托(delegate)中应包含此代码。如果您使用的是在早期版本的 Xcode 中创建的项目，则该行可能会丢失，并且您会收到警告消息。