Overriding view controller based status bar appearance

I have an app with view controller based status bar appearance set to YES. Some of my views have dark, some of my views have light content, and the app has a pretty complex view controller hierarchy, but it works perfectly with subclassing and overriding the appropriate methods combined with modal views capturing presentation styles etc).

However, I need a global way to view a specific item at top (behind status bar, inside my app bounds), just like the bar like personal hotspot/ GarageBand recording/in call etc bar at the top. Because of the bar's background color, I want to override the status bar appearance while displaying the bar (which can be displayed anywhere in the app so I subclassed UIWindow and put its presentation code and view directly there). The bar displays exactly as I wanted on screens with light content status bar (as my bar's text is white and background is dark) but looks terrible on dark content status bar (and no, I can't change the colors of the bar).

How can I override the "whatever the currently presented view controller is"'s preferred status bar style globally (of course, without traversing all instances of the status bar methods in all view controllers), while still using view controller based status bar appearance? My app targets iOS 8.0+.

Solution

I've ended up in a very hacky (but working) way. It might not work in every scenario, but it worked in mine. I've kept the view as it is, and haven't touched a single view or controller.

First, I've got the topmost view controller currently being displayed. I've used the code from iPhone -- How to find topmost view controller and modified it a little to handle navigation controller and tab bar controller cases too:

+ (UIViewController*) topmostControllerForViewController:(__kindof UIViewController*)topController
{
    while (topController.presentedViewController) {
        topController = topController.presentedViewController;
    }
    if([topController isKindOfClass:[UINavigationController class]]){
        UINavigationController *navController = topController;
        return [self topmostControllerForViewController:navController.visibleViewController];
    }
    if([topController isKindOfClass:[UITabBarController class]]){
        UITabBarController *tabController = topController;
        return [self topmostControllerForViewController:tabController.selectedViewController];
    }
    return topController;
}

+ (UIViewController*) topmostController
{
    __kindof UIViewController *topController = [UIApplication sharedApplication].keyWindow.rootViewController;
    return [self topmostControllerForViewController:topController];
}

Then I've created a view controller without a view (view is nil). In it's init method (does not work in first call if put in viewDidLoad: as it's called inside the transition process and it's too late), I've added the following:

self.modalPresentationCapturesStatusBarAppearance = YES;
self.modalPresentationStyle = UIModalPresentationOverCurrentContext;

That code allowed my "dummy" view(less) controller to handle all the presentation context, including status bar appaearance and what happens to the other views controllers when it's presented. When presented over current context, the view controller at the back is not removed from view hierarchy. If I don't do that, it will be removed and screen will be black (as I don't have any view and I want the previous view controller to be shown).

So far so good. Then, I've displayed my bar normally, but simultaneously, presented that view controller modally without any view. Because the view controller didn't have any view and was presented over the current context, it visually didn't appear in any way, but since it was a modal presentation and the dummy view controller was set to capture presentation style, it triggered iOS to ask my app for status bar style. I've simply set up my status bar style as I've wanted in the view controller methods.

There was a little problem. When I've presented the new view controller, system added a UITransitionView on top of my previous view controller. If there was an actual view, it would be on top of the transition view. The transition view is completely transparent, but it has user interaction enabled and captured all the touch events, making my app unresponsive until I've dismissed the controller. I needed my previous view controller to receive touch events. I've dug deeper and found where modal presentation adds the transition view, and removed it when presenting the view controller after transition animation is complete:

for (UIView *view in self.subviews) {
        NSString *className = NSStringFromClass([view class]);
        if([className hasPrefix:@"UIT"] && className.length == 16){
            //this must be UITransitionView, but I'm not using it directly since it may interfere with private API usage and get app rejected by Apple.
            //now, we need to find another transition view inside this and remove it
            for (UIView *innerView in view.subviews) {
                className = NSStringFromClass([innerView class]);
                if([className hasPrefix:@"UIT"] && className.length == 16){
                    //this is the transition view that we need to remove
                    [innerView removeFromSuperview];
                } 
            }
        }
}

Since UITransitionView is a private view type and I'm not sure if it causes a problem with App Store, I've done a heuristic check of UITransitionView by checking the first letters UIT and checking the length of the class name. It's not bulletproof, but it seems to work and unlikely to return false positive.

Everything now works as expected. It's hacky, and may break in the future, especially if modal presentation changes under the hood. But rest assured, it works.