Present Uialertcontroller from Appdelegate

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 + 1

let 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/

How to present UIAlertView from appDelegate

Ok i finally got it, you need to find the active VC using this before trying to present your alertController :

let navigationController = application.windows[0].rootViewController as UINavigationController
let activeViewCont = navigationController.visibleViewController
activeViewCont.presentViewController(alertController, animated: true, completion: nil)

How do I add a UIAlertController in app delegate (obj-c)

Per Apple Documentation, UIAlertController is just like any another view controller which needs a view controller as base to present on.

To present an UIAlertController from AppDelegate, you can create a temporary window with an empty view controller in it and present on top of it. Something like this:

self.alertWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
self.alertWindow.rootViewController = [[UIViewController alloc] init];
self.alertWindow.windowLevel = UIWindowLevelAlert + 1;
[self.alertWindow makeKeyAndVisible];
[self.alertWindow.rootViewController presentViewController:alertControl animated:YES completion:nil];

This window will automatically be taken out of memory once alert is dismissed.

You can also present your alert on rootViewController if it has been initialized and is added in view hierarchy.

I hope you got why you are getting this error now. Technically, AppDelegate is not a view controller and so does not respond to presentViewController:animated:completion: method.

UIAlertController not showing from AppDelegate

Alright, I solved this problem by creating a UIWindow object with an empty view controller and presenting my alert in it. Apparently, once alert controller is dismissed, this temporary window also go away.

self.alertWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
self.alertWindow.rootViewController = [[UIViewController alloc] init];
self.alertWindow.windowLevel = UIWindowLevelAlert + 1;
[self.alertWindow makeKeyAndVisible];
[self.alertWindow.rootViewController presentViewController:alertControl animated:YES completion:^{
    [aBlockSelf alertPresented];
}];

Thanks to this SO thread where a WWDC lab session is referred :-)!

Present alert from AppDelegate when app is ready for presenting an alert

You need applicationDidBecomeActive , but make sure it's called when you return from background also , so wrap code in once var if you don't like it to be called again

func applicationDidBecomeActive(_ application: UIApplication) {
    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}

Presenting Alert Controller from the delegate

Use below line:

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

Instead of

vc.present(alertController, animated: true, completion: nil)

than problem is solved.

Example:

DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.5, execute: {
        let alertController = UIAlertController(title: "Alert Title", message:
          "Message", preferredStyle: .actionSheet)

        let okAction = UIAlertAction(title: "Ok", style:.default) {
            UIAlertAction in
            NSLog("OK Pressed")
        }

        let cancelAction = UIAlertAction(title: "Cancel", style: .cancel) {
            UIAlertAction in
            NSLog("Cancel Pressed")
        }

        alertController.addAction(okAction)
        alertController.addAction(cancelAction)
        self.window?.rootViewController?.present(alertController, animated: true, completion: nil)
    })

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