On which ViewController should I implement FacebookSDK's removeObserver?

Question

I am implementing facebook's SDK for iOS into my app. There are two functions however that are supposed to register and unregister for the notifications:

From Facebook's login to facebook with ios:

in the viewDidLoad method, register for the session change notification you defined in the app delegate by adding this code to the end of the method:

[[NSNotificationCenter defaultCenter]
addObserver:self
selector:@selector(sessionStateChanged:)
name:FBSessionStateChangedNotification
object:nil];

and

Unregister for the notifications by adding the following code to the end of the didReceiveMemoryWarning the method:

[[NSNotificationCenter defaultCenter] removeObserver:self];

Since I have quite a few view controllers and all of them should be using facebook's API, I thought I should implement the register/unregister methods in the applicationDidFinishLoadingWithOptions (for register for notifications)

but I am not sure if and how I should implement the unregister's removeObserver command, because applicationDidReceiveMemoryWarning is not available for the AppDelegate.

Is DidReceiveMemoryWarning visiting all the viewControllers of the App?
Would it be sufficient to unregister in just one of my viewControllers ?

tarmes tarmes · Accepted Answer · 2012-11-07T16:33:49

The application delegate does receive memory warnings:

http://developer.apple.com/library/ios/#documentation/uikit/reference/UIApplicationDelegate_Protocol/Reference/Reference.html

If it didn't, another option would be to use the notification center:

NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
[center addObserver:self
           selector:@selector(whatever:)
               name:UIApplicationDidReceiveMemoryWarningNotification
             object:nil];

That all said, it seems to me that removing the observer on a memory warning is inappropriate. At what point will your reinstate it? But hey, if that's what Facebook recommends...

On which ViewController should I implement FacebookSDK's removeObserver?

1 Answers