In case it helps anyone, my issue was extremely silly. Totally my fault of course. A notification was triggering a method that was calling the modal. But I wasn't removing the notification correctly, so at some point, I would have more than one notification, so the modal would get called multiple times. Of course, after you call the modal once, the viewcontroller that calls it it's not longer in the view hierarchy, that's why we see this issue. My situation caused a bunch of other issue too, as you would expect.

总之，无论你做什么，都要确保模态不会被调用超过一次。

可能和我一样，你有一个错误的根viewController

我想在非uiviewcontroller上下文中显示一个ViewController，

所以我不能使用这样的代码:

[self presentViewController:]

我得到一个UIViewController

[[[[UIApplication sharedApplication] delegate] window] rootViewController]

由于某种原因(逻辑错误)，rootViewController是其他的东西比预期的(一个正常的UIViewController)。然后我纠正了这个错误，用UINavigationController替换了rootViewController，问题就解决了。

这适用于呈现任何视图控制器，如果你有可用的导航控制器。 self.navigationController ?。present(MyViewController, animated: true, completion: nil) 此外，我可以能够呈现警报和邮件控制器也。

我也有同样的问题。问题是，performSegueWithIdentifier是由通知触发的，只要我把通知放在主线程上，警告消息就消失了。

我通过将start()函数移动到解散完成块内部来修复它:

self.tabBarController.dismiss(animated: false) {
  self.start()
}

Start包含对self.present()的两个调用，一个用于UINavigationController，另一个用于UIImagePickerController。

这为我解决了问题。

在主窗口中，可能总是会出现与显示警报不兼容的过渡。为了允许在应用程序生命周期的任何时候显示警报，您应该有一个单独的窗口来完成这项工作。

/// independant window for alerts
@interface AlertWindow: UIWindow

+ (void)presentAlertWithTitle:(NSString *)title message:(NSString *)message;

@end

@implementation AlertWindow

+ (AlertWindow *)sharedInstance
{
    static AlertWindow *sharedInstance;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedInstance = [[AlertWindow alloc] initWithFrame:UIScreen.mainScreen.bounds];
    });
    return sharedInstance;
}

+ (void)presentAlertWithTitle:(NSString *)title message:(NSString *)message
{
    // Using a separate window to solve "Warning: Attempt to present <UIAlertController> on <UIViewController> whose view is not in the window hierarchy!"
    UIWindow *shared = AlertWindow.sharedInstance;
    shared.userInteractionEnabled = YES;
    UIViewController *root = shared.rootViewController;
    UIAlertController *alert = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];
    alert.modalInPopover = true;
    [alert addAction:[UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
        shared.userInteractionEnabled = NO;
        [root dismissViewControllerAnimated:YES completion:nil];
    }]];
    [root presentViewController:alert animated:YES completion:nil];
}

- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];

    self.userInteractionEnabled = NO;
    self.windowLevel = CGFLOAT_MAX;
    self.backgroundColor = UIColor.clearColor;
    self.hidden = NO;
    self.rootViewController = UIViewController.new;

    [NSNotificationCenter.defaultCenter addObserver:self
                                           selector:@selector(bringWindowToTop:)
                                               name:UIWindowDidBecomeVisibleNotification
                                             object:nil];

    return self;
}

/// Bring AlertWindow to top when another window is being shown.
- (void)bringWindowToTop:(NSNotification *)notification {
    if (![notification.object isKindOfClass:[AlertWindow class]]) {
        self.hidden = YES;
        self.hidden = NO;
    }
}

@end

在设计上总是成功的基本用法:

[AlertWindow presentAlertWithTitle:@"My title" message:@"My message"];