AppDelegate、rootViewController 和 PresentViewController

我正在做 Facebook 集成教程，如果用户具有当前状态的有效令牌，我想显示我的 MainViewViewController，否则我想显示 LoginViewController。

MainView AppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    if (FBSession.activeSession.state == FBSessionStateCreatedTokenLoaded) {
        // To-do, show logged in view
    } else {
        // No, display the login page.
        [self showLoginView];
    }
    return YES;
}
- (void)showLoginView
{
    UIStoryboard *mainstoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard"          bundle:nil];
    LoginViewController* loginViewController = [mainstoryboard      instantiateViewControllerWithIdentifier:@"LoginViewController"];
    [self.window.rootViewController presentViewController:loginViewController animated:YES completion:NULL];
}

控制台错误：

Warning: Attempt to present <LoginViewController: 0xb492fd0> on <MainViewViewController: 0xb1bd820> whose view is not in the window hierarchy!

我不想使用导航控制器。

我遇到过同样的问题。根据以下问题的答案这个问题，我补充说[self.window makeKeyAndVisible]就在之前presentViewController:animated:completion:，这为我解决了这个问题。

在你的情况下， showLoginView 变成

- (void)showLoginView
{
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
    LoginViewController *loginViewController = [storyboard instantiateViewControllerWithIdentifier:@"LoginViewController"];
    [self.window makeKeyAndVisible];
    [self.window.rootViewController presentViewController:loginViewController animated:YES completion:NULL];
}