How to show UIAlertController from Appdelegate

try this

Objective-C

UIWindow* topWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];topWindow.rootViewController = [UIViewController new];topWindow.windowLevel = UIWindowLevelAlert + 1;UIAlertController* alert = [UIAlertController alertControllerWithTitle:@"APNS" message:@"received Notification" preferredStyle:UIAlertControllerStyleAlert];[alert addAction:[UIAlertAction actionWithTitle:NSLocalizedString(@"OK",@"confirm") style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {    // continue your work    // important to hide the window after work completed.    // this also keeps a reference to the window until the action is invoked.    topWindow.hidden = YES; // if you want to hide the topwindow then use this    topWindow = nil; // if you want to remove the topwindow then use this }]];[topWindow makeKeyAndVisible];[topWindow.rootViewController presentViewController:alert animated:YES completion:nil];

Swift3 and above

var topWindow: UIWindow? = UIWindow(frame: UIScreen.main.bounds)topWindow?.rootViewController = UIViewController()topWindow?.windowLevel = UIWindow.Level.alert + 1let alert = UIAlertController(title: "APNS", message: "received Notification", preferredStyle: .alert)alert.addAction(UIAlertAction(title: "OK", style: .cancel) { _ in    // continue your work    // important to hide the window after work completed.    // this also keeps a reference to the window until the action is invoked.    topWindow?.isHidden = true // if you want to hide the topwindow then use this    topWindow = nil // if you want to hide the topwindow then use this })topWindow?.makeKeyAndVisible()topWindow?.rootViewController?.present(alert, animated: true, completion: nil)

Detail description: http://www.thecave.com/2015/09/28/how-to-present-an-alert-view-using-uialertcontroller-when-you-dont-have-a-view-controller/

Shortest & Simplest :

Create a extension :

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} }

and then use it anywhere like

UIApplication.topViewController()?.present(UIViewController, animated: true, completion: nil)

With this you can present Alert or anything AnywhereExample :

let alert = UIAlertController(title: "Your title", message: "Your message", preferredStyle: .alert)let cancelButton = UIAlertAction(title: "Ok", style: .cancel, handler: nil)alert.addAction(cancelButton)UIApplication.topViewController()?.present(alert, animated: true, completion: nil)

ALTERNATE METHOD :

No need to create any Extension or any method or anything simply write the above 3 lines for creating an Alert and for presenting use :

self.window?.rootViewController?.present(alert, animated: true, completion: nil)

That's it.! =)

Anbu.Karthik's answer but inSwift 4.1

var topWindow: UIWindow? = UIWindow(frame: UIScreen.main.bounds)topWindow?.rootViewController = UIViewController()topWindow?.windowLevel = UIWindowLevelAlert + 1let alert: UIAlertController =  UIAlertController(title: "APNS", message: "received Notification", preferredStyle: .alert)    alert.addAction(UIAlertAction.init(title: "OK", style: .default, handler: { (alertAction) in        topWindow?.isHidden = true        topWindow = nil    }))topWindow?.makeKeyAndVisible()topWindow?.rootViewController?.present(alert, animated: true, completion:nil)

Thanks for reading this.