Calling a method when the application is called from background

Question

In applications like Foursquare when I click the Home button the application goes to background. Then when I click on its icon, it loads back the content on the screen.

When I send my app to background and then I recall it back, it doesn't load back the content to the screen. I have entered my code in the viewDidAppear method but it is not executed.

How is it possible to load the application content when it becomes active?

Read the docs: http://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html#//apple_ref/doc/uid/TP40007072-CH4-SW3 — dasdom, Jan 26 '12 at 16:35

score 5 · Answer 1 · answered Jan 26 '12 at 16:35

5

You need to respond to - (void)applicationDidBecomeActive:(UIApplication *)application or - (void)applicationWillEnterForeground:(UIApplication *)application or the equivalent UIApplication notifications. The UIViewController lifecycle calls like viewDidAppear aren't triggered by app lifecycle transitions.

answered Jan 26 '12 at 16:35

smparkes

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This is already in my AppDelegate. So just adding the code there worked. Thanks. – Todd Horst Feb 12 '14 at 15:28

score 3 · Answer 2 · answered Jan 26 '12 at 16:45

smparkes suggestion is right. You could register for UIApplicationDidBecomeActiveNotification or UIApplicationWillEnterForegroundNotification. These notifications are called after those method (the ones smparkes wrote) are called. In the handler for this notification do what you want. For example in viewDidLoad for your controller register the following notification:

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(doUpdate:)
                                             name:UIApplicationDidBecomeActiveNotification object:nil];

Do not forget to remove in dealloc:

[[NSNotificationCenter defaultCenter] removeObserver:self];

Finally, doUpdate method could be the following

-(void)doUpdate:(NSNotification*)note
{
    // do your stuff here...
}

I suggest you to read UIApplicationDelegate class reference. In particular read about Monitoring Application State Changes.

Hope it helps.

I am using ARC, so do i still have to dealloc it ? and why ? — sharon, Jan 26 '12 at 17:10
You should.For more info read this [stackoverflow topic](http://stackoverflow.com/questions/8372841/removing-a-nsnotificationcenter-observer-in-ios-5-arc). In this other [stackoverflow topic](http://stackoverflow.com/questions/6469209/objective-c-where-to-remove-observer-for-nsnotification) instead the explanation why you should remove it. Hope it helps. — Lorenzo B, Jan 26 '12 at 17:25

score 0 · Answer 3 · answered Jan 18 '15 at 12:24

Suppose you want to listen to UIApplicationDidBecomeActiveNotification,here is the ObjC code that might help you.

[[NSNotificationCenter defaultCenter] addObserverForName:UIApplicationDidBecomeActiveNotification
object:nil queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification *note) {

    // custom code goes here.
}];

Calling a method when the application is called from background

3 Answers3