calling ViewController's member function from AppDelegate

Question

I want to call a ViewController's member function in AppDelegate's applicationWillResignActive function. Not sure what is the best way to do so. I tried doing so this way:

let landmark = LandmarkViewController()
landmark.test()

but it somehow doesn't seem right. I'm essentially creating new instance of the controller instead of using the already existent one.

This may be a good place to send a notification via the [notification center](https://developer.apple.com/reference/foundation/nsnotificationcenter). That your `LandmarkViewController` can be an observer of. — hola, Mar 23 '17 at 10:13
Are you using storyboard? if Yes, this is the [answer](http://stackoverflow.com/questions/41136597/create-singleton-of-a-viewcontroller-in-swift-3/41136939#41136939) of what are you looking for :) — Ahmad F, Mar 23 '17 at 10:13

tanz · Accepted Answer · 2017-03-23T13:38:02.277

6

I think the best way to achieve what you want is to set an observer for this notification UIApplicationWillResignActiveNotification into your view controller itself.

override func viewDidLoad() {
    super.viewDidLoad()
    let notificationCenter = NotificationCenter.default
    notificationCenter.addObserver(self, selector: #selector(appDidResign), name: Notification.Name.UIApplicationWillResignActive, object: nil)
}

func appDidResign() {
    // do your stuff
}

deinit {
    NotificationCenter.default.removeObserver(self) //always remember to remove any observers (you can do this in deinit in this case)
}

edited Mar 23 '17 at 13:38

answered Mar 23 '17 at 10:16

tanz

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Well, I think this is not what OP is asking for, anyway it might be a goo approach... – Ahmad F Mar 23 '17 at 10:17
That's true. Although I think the OP is asking this because is not aware of the Notification :) – tanz Mar 23 '17 at 10:18
I'd suggest to -also- add the code that related to posting the notification. – Ahmad F Mar 23 '17 at 10:31
@AhmadF This notification is posted by the system, you don't need to post it yourself. – tanz Mar 23 '17 at 13:39
Oh, I see... sorry, I think that I really to sleep :) – Ahmad F Mar 23 '17 at 13:47

Fahim · Answer 2 · 2017-03-23T10:15:07.780

0

Yes, your above code will create a new instance. If you want to use an existing instance, then you'd need to get a reference to the existing instance somehow.

How you get the reference would depend on how you have your view controllers set. For example, if your LandmarkViewController is the root view controller, you can get it via your UIWindow, perhaps. Or, when your LandmarkViewController instance is created, you can pass a reference to the view controller to the app delegate. It all depends on how your app is set up.

edited Mar 23 '17 at 10:15

answered Mar 23 '17 at 10:13

Fahim

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This should be a comment – Ahmad F Mar 23 '17 at 10:13
Why should it be a comment? I was answering his question :) – Fahim Mar 23 '17 at 10:15

score 0 · Answer 3 · answered Mar 23 '17 at 10:18

0

You can get the rootViewController (which your LandmarkViewController is how I understood) from the UIWindow:

if let rootViewController = self.window?.rootViewController as LandmarkViewController {
    rootViewController.test()

}

answered Mar 23 '17 at 10:18

shallowThought

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score 0 · Answer 4 · answered Mar 23 '17 at 10:19

I think best way is add observer for notification in this class. Some think like this:

class LandmarkViewController: ...
{
   ...
   func viewDidLoad()
   {
      ...
      NotificationCenter.default.addObserver(forName: applicationWillResignActive, object: nil, queue: OperationQueue.main) { (notification) in
           ...
      }
   }
}

calling ViewController's member function from AppDelegate

4 Answers4