ios - 在 didFinishLaunching 上自定义 View Controller 堆栈

Question

我正在尝试使用以下代码在首次启动时为我的应用程序提供教程/登录/介绍 View Controller :

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

    UIViewController *firstController = [[UIViewController alloc] init];
    [self.window setRootViewController:firstController];

    if ([self shouldShowIntro]) {
        IntroViewController *introViewController = [[IntroViewController alloc] init];
        [firstController presentViewController:introViewController animated:NO completion:nil];
    }

    return YES;
}

这很好用，但是会出现令人讨厌的视觉效果...在您看到 IntroViewController 之前，有一瞬间， firstController可见。我尝试展示 IntroViewController在设置窗口的 rootViewController 之前，但这(并不奇怪)会导致以下警告:
Warning: Attempt to present <IntroViewController: 0x7fd8eb3362f0> on <UIViewController: 0x7fd8eb335180> whose view is not in the window hierarchy!
如何在没有这种烦人的视觉闪光的情况下以模态方式呈现 IntroViewController？我要 IntroViewController在启动屏幕消失后已经显示并且能够以模态方式关闭。

Answer 1

以下适用于我，在 iPhone 6 和模拟器上的 iOS 8.1 上运行时没有闪烁。我使用了 SDK 8.1 版，我认为您的 SDK 级别不同，因为我得到的警告和结果与使用您提供的代码不同。

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

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

    UIViewController *firstController = [[UIViewController alloc] init];
    firstController.view.backgroundColor = [UIColor blueColor];
    [self.window setRootViewController:firstController];

    dispatch_async(dispatch_get_main_queue(), ^{
        UIViewController* modalViewController = [[UIViewController alloc] init];
        modalViewController.view.backgroundColor = [UIColor grayColor];
        [firstController presentViewController: modalViewController animated: NO completion: nil];
    });

    // dismiss after a few seconds..
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [firstController dismissViewControllerAnimated: YES completion: nil];
    });

    return YES;
}

更新 使用MMDrawerController:

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

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

    MMDrawerController *drawerController = [[MMDrawerController alloc] init];
    drawerController.centerViewController = [[UIViewController alloc] init];
    drawerController.centerViewController.view.backgroundColor = [UIColor blueColor];
    drawerController.rightDrawerViewController = [[UIViewController alloc] init];
    drawerController.rightDrawerViewController.view.backgroundColor = [UIColor greenColor];
    drawerController.openDrawerGestureModeMask = MMOpenDrawerGestureModeAll;
    drawerController.closeDrawerGestureModeMask = MMOpenDrawerGestureModeAll;

    [self.window setRootViewController:drawerController];

    dispatch_async(dispatch_get_main_queue(), ^{
        UIViewController* modalViewController = [[UIViewController alloc] init];
        modalViewController.view.backgroundColor = [UIColor grayColor];
        [drawerController presentViewController: modalViewController animated: NO completion: nil];
    });

    // dismiss after a few seconds..
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [drawerController dismissViewControllerAnimated: YES completion: nil];
    });

    return YES;
}

此外，根据您的评论，听起来好像预加载 View 是关键。在演示之前尝试调用 [firstController view] 和 [modalController view] 以确保它们已加载。