How to create a reference to on of my view controllers from my app delegate?

Hi I was wondering, how can I create a reference to one o开发者_开发知识库f my view controllers from my app delegate? I'd like to call a specific method (of my view controller) from the delegate when my app enters foreground.

1. Make an member ivar pointer of the same class in your *AppDelegate, set it to nil when launching, set its property to "assign".

2. When the specific view controller is created and loaded in the memory, in this controller's viewDidLoad method:

   [[[UIApplication sharedApplication] delegate] setThatSpecialContrller:self];

3. When this controller has to be deallocated at some point, you use a similar line of code to again set the pointer to nil.

4. Do a check every time your app is coming from the background to the foreground, if the pointer is not nil, use this not-nil reference to call your specific controller and its method.

Alternatively, you can listen for the UIApplicationWillEnterForegroundNotification notification.

- (void)viewDidLoad {
    NSNotificationCenter *defaultCenter = [NSNotificationCenter defaultCenter];
    [defaultCenter addObserver:self selector:@selector(applicationWillEnterForeground:) UIApplicationWillEnterForegroundNotification object:nil];
}

- (void)viewDidUnload {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

Alternative approach, that diwup mentioned, is nicely and shortly described in section "Hooking Up The Left With the Right" in this tutorial.