ios UIApplication extension function to get the UIViewController in flutter plugin

ShareSheet.swift

var sharedItems : Array<NSObject> = Array()
          
sharedItems.append((message as NSObject?)!)

let activityViewController = UIActivityViewController(activityItems: sharedItems, applicationActivities: nil)

activityViewController.setValue("Share", forKeyPath: "subject");

DispatchQueue.main.async {
    UIApplication.topViewController()?.present(activityViewController, animated: true, completion: nil)
}

UIApplication.swift

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
    }
}