dismissViewControllerAnimated:completion: on iOS 8

Question

In iOS <= 7, directly after calling dismissViewControllerAnimated:completion: would result in presentedViewController being nil. In iOS 8, presentedViewController still points to the presented viewcontroller, right until the completion block is executed.

[self dismissViewControllerAnimated:NO completion:^{
    //self.presentedViewController is nil
}];
//self.presentedViewController is nil on iOS 7, but not nil on iOS 8

So in iOS 8 we cannot rely on the property presentedViewController in order to find out which viewcontroller is currently the top visible viewcontroller.

In iOS 8, alerts need to be presented onto a viewcontroller (which poses another problem). They will not show if the viewcontroller we try to present on already presents a viewcontroller.

If I just dismissed my presented viewcontroller and show a UIAlertController on the currently top visible viewcontroller (by recursively searching for the last presentedViewController), then it will of course not show but log an error message: "Warning: Attempt to present on whose view is not in the window hierarchy!"

1. Is this a bug in iOS 8 or just the new way?
2. How can I find out the viewcontroller I can present my UIALertController on?

Answer 1

I found a workaround to find out which viewcontroller I can present the alert upon:

@implementation UIViewController (visibleViewController)

- (UIViewController *)my_visibleViewController {

    if ([self isKindOfClass:[UINavigationController class]]) {
        // do not use method visibleViewController as the presentedViewController could beingDismissed
        return [[(UINavigationController *)self topViewController] my_visibleViewController];
    }

    if ([self isKindOfClass:[UITabBarController class]]) {
        return [[(UITabBarController *)self selectedViewController] my_visibleViewController];
    }

    if (self.presentedViewController == nil || self.presentedViewController.isBeingDismissed) {
        return self;
    }

    return [self.presentedViewController my_visibleViewController];
}

@end

// To show a UIAlertController, present on the following viewcontroller:
UIViewController *visibleViewController = [[UIApplication sharedApplication].delegate.window.rootViewController my_visibleViewController];

Swift 3:

import UIKit

extension UIViewController {
    func visibleViewController() -> UIViewController? {
        guard !(self is UINavigationController) else {
            let navVC = self as! UINavigationController
            return navVC.topViewController?.visibleViewController()
        }

        guard !(self is UITabBarController) else {
            let tabVC = self as! UITabBarController
            return tabVC.selectedViewController?.visibleViewController()
        }

        if self.presentedViewController == nil || 
           self.presentedViewController!.isBeingDismissed {
            return self
        }

        return self.presentedViewController?.visibleViewController()
    }
}