如何在应用启动时以模态方式呈现视图控制器？

Question

我创建了一个仅在我的应用首次启动时出现的屏幕；效果很好。但是，我想在我的根视图控制器顶部以模态方式呈现此屏幕（EditorsNoteViewController 是我想在首次启动时以模态方式呈现的屏幕）。有谁知道我会怎么做？这是我目前所拥有的：

Appdelegate.m

        - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
        {
            self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
            if ([[NSUserDefaults standardUserDefaults] boolForKey:@"HasLaunchedOnce"])
            {
                NSLog(@"not first launch");

                      self.viewController = [[UIStoryboard storyboardWithName:@"Main_iPhone" bundle:nil] instantiateViewControllerWithIdentifier:@"articlesNav"];
                self.window.rootViewController = self.viewController;

            }
            else
            {
                [[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"HasLaunchedOnce"];
                [[NSUserDefaults standardUserDefaults] synchronize];



                self.viewController = [[UIStoryboard storyboardWithName:@"Main_iPhone" bundle:nil] instantiateViewControllerWithIdentifier:@"articlesNav"];
                self.window.rootViewController = self.viewController;


     EditorsNoteViewController *vc = [[EditorsNoteViewController alloc]init];
             [self.viewController.navigationController presentViewController:vc animated:YES completion:nil];

}
                [self.window makeKeyAndVisible];
    return YES;
}

Answer 1

我知道你必须打电话给

[self.window makeKeyAndVisible];

在呈现视图控制器之前

Answer 2

我已经多次阅读并遇到过这个问题。完全解决此问题的一种方法（没有任何闪烁或警告）是考虑将包含您的根视图控制器和模态呈现的视图控制器的自定义容器视图控制器作为子视图控制器。然后容器视图控制器可以使用自定义动画在两者之间转换，效果与呈现/关闭非常相似。

让我们考虑以下容器视图控制器：

@implementation ContainerViewController {
    NSMutableArray* stack;
}

- (instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) {
        stack = [NSMutableArray new];
    }
    return self;
}

- (void) pushViewController:(UIViewController*) viewController {
    UIViewController* currentViewController = [stack lastObject];
    [stack addObject:viewController];
    if (self.isViewLoaded) {
        [self addChildViewController:viewController];
        [currentViewController willMoveToParentViewController:nil];
        viewController.view.frame = CGRectOffset(self.view.bounds, 0, self.view.bounds.size.height);
        [self transitionFromViewController:currentViewController toViewController:viewController duration:0.3   options:kNilOptions animations:^{
            viewController.view.frame = self.view.bounds;
        } completion:^(BOOL finished) {
            [viewController didMoveToParentViewController:self];
            [currentViewController removeFromParentViewController];
        }];
    }
}

- (void) popViewController {
    UIViewController* currentViewController = [stack lastObject];
    [stack removeLastObject];
    if (self.isViewLoaded) {
        UIViewController* viewController = [stack lastObject];
        [self addChildViewController:viewController];
        [currentViewController willMoveToParentViewController:nil];
        [self transitionFromViewController:currentViewController toViewController:viewController duration:0.3   options:kNilOptions animations:^{
            [self.view sendSubviewToBack:viewController.view];
            currentViewController.view.frame = CGRectOffset(self.view.bounds, 0, self.view.bounds.size.height);
        } completion:^(BOOL finished) {
            [viewController didMoveToParentViewController:self];
            [currentViewController removeFromParentViewController];
        }];
    }
}

- (void)viewDidLoad {
    [super viewDidLoad];
    UIViewController* viewController = [stack lastObject];
    [self addChildViewController:viewController];
    [self.view addSubview:viewController.view];
    [viewController didMoveToParentViewController:self];
}

@end

在您的 AppDelegate 中，您可以按照这些思路进行操作：

ContainerViewController* viewController = [ContainerViewController new];
[viewController pushViewController: [RootViewController new];

if ([self shouldPresentModalViewController]) {
    [viewController pushViewController: [ModalViewController new];
}

self.window.rootViewController = self.viewController;
[self.window makeKeyAndVisible];

在模态视图控制器的某处，您可以使用以下代码将其关闭：

[((ContainerViewController*) self.parentViewController) popViewController];

Answer 3

假设您已经在情节提要中创建了 EditorsNoteViewController，您应该像这样初始化它：

UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
EditorsNoteViewController *vc = (EditorsNoteViewController*)[storyboard instantiateViewControllerWithIdentifier:@"EditorsNoteOrWhateverIdentifierYouChose"];

尝试检查您的 RootViewController -viewDidLoad 中的 NSUserDefaults，如果是第一次，请在此处显示新的 UIViewController（这样您就不需要弄乱您的 AppDelegate）。

如果你想以动画形式呈现它，你可以在 -viewDidAppear 而不是 -viewDidLoad 中做到这一点。