我有一个在启动时实现 Facebook 登录的应用程序，使用的代码与此非常相似：Facebook Scrumptious Tutorial，除了 Storyboards。
代码的基本要点是，在应用程序启动时，应用程序委托会检查您是否已经登录，如果是，它会直接进入主视图，如果没有，它会要求主视图显示登录信息查看以便用户可以登录。
我已经解决了我的另一个问题，即能够告诉故事板中的主视图呈现不同的视图，方法是从视图层次结构中获取主视图，然后在视图上调用 segue。一切正常，但是我还有最后一个问题要解决：
据我所知，应用程序 didFinishLaunchingWithOptions方法应该在情节提要完全加载后调用。但是在我的代码中，如果我尝试告诉主视图呈现另一个视图，它会给我一个错误，基本上说它尚未加载（警告：尝试在 <UINavigationController: 0xa28c6e0> 上呈现 <QLoginViewController: 0x955c020> 其视图不在窗口层次结构中！）。
但是，如果我告诉它延迟后呈现视图：
[self performSelector:@selector(showLoginViewAnimated:) withObject:NO afterDelay:.001];
（其中showLoginViewAnimated:是告诉主视图呈现登录视图的方法），然后它工作正常。
谁能帮我弄清楚这里出了什么问题，以及我该如何解决它？延迟执行选择器显然是一个不好的解决方法，因为我永远不知道不同的设备是否可能需要更长的时间来加载视图......
这是我的 appDelegate didFinishLaunchingWithOptions代码：
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
// Override point for customization after application launch.
self.navigationController = (UINavigationController *)self.window.rootViewController;
// Navigation Bar Color
[[UINavigationBar appearance] setTintColor:[UIColor colorWithRed:255.0/255.0 green:128.0/255.0 blue:60.0/255.0 alpha:1.0]];
/* Facebook Login */ // THIS IS THE RELEVANT CODE:
// See if we have a valid token for the current state
if (FBSession.activeSession.state == FBSessionStateCreatedTokenLoaded) {
// Yes, valid token exists - open the session (don't display login page)
[self openSession];
} else {
// No, valid token does not exist - display the login page.
if ([self.navigationController isViewLoaded]) {
[self showLoginViewAnimated:NO]; // MY ATTEMPT TO AVOID USING THE DELAY IF POSSIBLE
}
else {
[self performSelector:@selector(showLoginViewAnimated:) withObject:NO afterDelay:.001]; // Delay needed to allow for storyboard loading
}
}
return YES;
}
这是showLoginViewAnimated:代码：
- (void)showLoginViewAnimated:(BOOL)animated
{
UIViewController *topViewController = [self.navigationController topViewController];
UIViewController *presentedViewController = [topViewController presentedViewController];
// If the login screen is not already displayed, display it. If the login screen is
// displayed, then getting back here means the login in progress did not successfully
// complete. In that case, notify the login view so it can update its UI appropriately.
if (![presentedViewController isKindOfClass:[QLoginViewController class]]) {
if (animated) {
[topViewController performSegueWithIdentifier:@"ShowLoginViewAnimated" sender:self];
}
else {
[topViewController performSegueWithIdentifier:@"ShowLoginViewStatic" sender:self];
}
}
else {
QLoginViewController *loginViewController = (QLoginViewController *)presentedViewController;
[loginViewController loginFailed];
}
}
在应用程序的原始非故事板版本中，在我手动创建视图之前，不会在应用程序 didFinishLaunchingWithOptions中调用showLoginViewAnimated:方法：
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
self.viewController = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
self.navController = [[UINavigationController alloc] initWithRootViewController:self.viewController];
self.window.rootViewController = self.navController;
[self.window makeKeyAndVisible];
因此，在我尝试告诉他们呈现新视图之前，我已经 100% 确定视图存在。然而，在应用程序的情节提要版本中，不存在任何代码，所以我只需要相信理论上应用程序 didFinishLaunchingWithOptions方法在情节提要视图完全加载之前不会被调用 - 但是，情况似乎并非如此. 也许它是异步执行的？我不知道...
有任何想法吗？谢谢你的帮助！
编辑：这是教程中的原始代码，它工作得非常好 - 并且几乎完全相同，只是使用笔尖。我在我的代码中将(BOOL)animated参数添加到showLoginView方法中，但这是为了别的，并没有改变任何东西（我已经检查过了）。
这是原始（非故事板）appDelegate didFinishLaunchingWithOptions方法：
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
self.viewController = [[FBLViewController alloc] initWithNibName:@"FBLViewController" bundle:nil];
self.navController = [[UINavigationController alloc] initWithRootViewController:self.viewController];
self.window.rootViewController = self.navController;
[self.window makeKeyAndVisible];
// See if we have a valid Facebook token for the current state
if (FBSession.activeSession.state == FBSessionStateCreatedTokenLoaded) {
// Yes, so just open the session (this won't display any UX).
[self openSession];
}
else {
// No, display the login page.
[self showLoginView];
}
return YES;
}
这是原始（非故事板）showLoginView方法：
- (void)showLoginView
{
UIViewController *topViewController = [self.navController topViewController];
UIViewController *presentedViewController = [topViewController presentedViewController];
// IF the login screen is not already displayed, display it. If the login screen is
// displayed, then getting back here means the login in progress did not successfully
// complete. In that case, notify the login view so it can update its UI appropriately.
if (![presentedViewController isKindOfClass:[FBLLoginViewController class]]) {
FBLLoginViewController *loginViewController = [[FBLLoginViewController alloc] initWithNibName:@"FBLLoginViewController" bundle:nil];
loginViewController.delegate = self;
[topViewController presentViewController:loginViewController animated:NO completion:nil];
}
else {
FBLLoginViewController *loginViewController = (FBLLoginViewController *)presentedViewController;
[loginViewController loginFailed];
}
}