Get visible view controller in paging UIScrollView

Question

Note:

• I am not using a UINavigationController.
• I have a UIViewController called ContainerViewController which has 3 child view controllers that acts similar to a UIPageViewController, but it is not a UIPageViewController, it's contains a paging UIScrollView instead. Each child view controller then is able to instantiate other view controller's modally.

I want to refresh a view controller when coming back from the background. However, this should only happen if when you return from the background, that view controller is the visible one (meaning top most and active).

Question is: How do I determine if a view controller is the one that is visible (top most and active on screen now)?

If I use an answer from this question: Get top most UIViewController

extension UIApplication {
    class func topViewController(controller: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
        if let navigationController = controller as? UINavigationController {
            return topViewController(controller: navigationController.visibleViewController)
        }
        if let tabController = controller as? UITabBarController {
            if let selected = tabController.selectedViewController {
                return topViewController(controller: selected)
            }
        }
        if let presented = controller?.presentedViewController {
            return topViewController(controller: presented)
        }
        return controller
    }
}

This works. But if I leave the app in a child view controller of ContainerViewController, this extension just returns ContainerViewController -> not the child view controller.

Any thoughts?

Answer 1

You know you're going to need this information, so it's just a matter of planning ahead. Each time you switch pages in the scroll view, use your knowledge of the child view controllers and the pages to record, in a property of the container view controller, what view controller's view is showing now. Now all your routine has to do is consult that property.