[iOS] How to get top most view controller?
+ (UIViewController *)topViewController {     return [self topViewController:[UIApplication sharedApplication].keyWindow.rootViewController]; }  + (UIViewController *)topViewController:(UIViewController *)rootViewController {     if (rootViewController.presentedViewController == nil) {         return rootViewController;     }     if ([rootViewController.presentedViewController isKindOfClass:[UINavigationController class]]) {         UINavigationController *navigationController = (UINavigationController *)rootViewController.presentedViewController;         UIViewController *lastViewController = [[navigationController viewControllers] lastObject];         return [self topViewController:lastViewController];     }     UIViewController *presentedViewController = (UIViewController *)rootViewController.presentedViewController;     return [self topViewController:presentedViewController]; }  + (UINavigationController *)navigationController {     UIViewController *topViewController = [self topVi...