UINavigationController with presented UIAlertController gets additionally dismissed

Question

I've got this UIAlertController that I present modally on top of the topmost view controller like so:

UIViewController *top = [Utility topController];

UIAlertController *alertController
= [UIAlertController alertControllerWithTitle:@"Error"
                                      message:@"input string too long"
                               preferredStyle:UIAlertControllerStyleAlert];

UIAlertAction *ok = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
  }];

[alertController addAction:ok];

UIAlertAction *cancel = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
  }];

[alertController addAction:cancel];

[top presentViewController:alertController
                  animated:true
                completion:nil];
}

The way I find the topmost view controller is by looping through the presented view controllers and by making sure I don't present on top of an alert controller:

+ (UIViewController *)topController {
  UIViewController *topController = [[[[UIApplication sharedApplication] delegate] window] rootViewController];

  while (topController.presentedViewController) {
    if ([topController.presentedViewController class] == [UIAlertController class]) {
      [topController.presentedViewController dismissViewControllerAnimated:YES completion:nil];
      break;
    }
    topController = topController.presentedViewController;
  }
  return topController;
}

This is all well and good and whatever UIViewController the top controller is presents the UIAlertController as it's presentedViewController. When I tap ok or cancel, the UIAlertController is implicitly dismissed. However, I have a custom UINavigationController that it gets presented on top of and for some reason that UINavigationController also has it's overridden dismissViewControllerAnimated: get called.

- (void)dismissViewControllerAnimated:(BOOL)flag completion:(void (^)(void))completion {
    [super dismissViewControllerAnimated:flag completion:completion];
}

Why is it that that UINavigationController has it's presentedViewController dismissed as well as itself? I should add that I present the UINavigationController like so:

[self presentViewController:nav animated:YES completion:nil];

Why is it that dismissViewControllerAnimated: seems to get called twice? Shouldn't the implicit call to dismissViewControllerAnimated only get called on the UINavigationController's presentedViewController which is the UIAlertController?

CodeWriter23 CodeWriter23 · Accepted Answer · 2017-10-15T04:41:24

You're calling dismissViewController in your "top" code, which doesn't make any sense to me at all.

Whatever is presenting any UIAlertController should return after displaying the alert, so there should only be one UIAlertController active at any given point in time, thus no need to dismiss a previous UIAlertController while trying to find the topmost viewController to display a new UIAlertController. You don't want to arbitrarily dismiss an alert for the user; your app needed to tell the user something, so let them decide when they're done reading it.

Suggest changes:

Use a category for finding the current viewController

@implementation UIViewController (Current)

#import "UIViewController+Current.h"

@implementation UIViewController (Current)

+(UIViewController*) findBestViewController:(UIViewController*)vc {

    if (vc.presentedViewController) {

        // Return presented view controller
        return [UIViewController findBestViewController:vc.presentedViewController];

    } else if ([vc isKindOfClass:[UISplitViewController class]]) {

        // Return right hand side
        UISplitViewController* svc = (UISplitViewController*) vc;
        if (svc.viewControllers.count > 0)
            return [UIViewController findBestViewController:svc.viewControllers.lastObject];
        else
            return vc;

    } else if ([vc isKindOfClass:[UINavigationController class]]) {

        // Return top view
        UINavigationController* svc = (UINavigationController*) vc;
        if (svc.viewControllers.count > 0)
            return [UIViewController findBestViewController:svc.topViewController];
        else
            return vc;

    } else if ([vc isKindOfClass:[UITabBarController class]]) {

        // Return visible view
        UITabBarController* svc = (UITabBarController*) vc;
        if (svc.viewControllers.count > 0)
            return [UIViewController findBestViewController:svc.selectedViewController];
        else
            return vc;

    } else {

        // Unknown view controller type, return last child view controller
        return vc;

    }

}
+(UIViewController*) currentViewController {
    // Find best view controller
    UIViewController* viewController = [UIApplication sharedApplication].keyWindow.rootViewController;
    return [UIViewController findBestViewController:viewController];
}

.h file

#import <UIKit/UIKit.h>

@interface UIViewController (Current)

+(UIViewController*) currentViewController;

@end

Then change your "top" line to use it

UIViewController *top = [UIViewController currentViewController];

UINavigationController with presented UIAlertController gets additionally dismissed

1 Answers