iOS app applicationWillEnterForeground and it stuck for a while

Question

I add this function to post a notification when the app enter foreground:

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    [[NSNotificationCenter defaultCenter] postNotificationName: @"UIApplicationWillEnterForegroundNotification" object: nil];
}

In my own class:

- (void) handleEnterForeground: (NSNotification*) sender
{
    [self reloadTableData];
}


- (void)viewDidLoad
{
    [super viewDidLoad];
    [[NSNotificationCenter defaultCenter] addObserver: self
                                         selector: @selector(handleEnterForeground:)
                                             name: @"UIApplicationWillEnterForegroundNotification"
                                           object: nil];
}

but the handleEnterForeground: function will called twice, I don't know why. The reloadTableData: function will call remote webService , so when the app enter foreground, it will stuck for a while.

Anallise

Answer 1

The system will call that event automatically. The reason it fires twice is because you manually fire it again.

P.S. It's better to use the variable name UIApplicationWillEnterForeground, instead of a NSString literal.

EDIT: I realize now the confusion is coming from the fact that you didn't know that this even name was already taken. As a note to other people who run into this kind of problem, it is a good practice to prefix your event names with your project prefix (i.e. XYZEventNotification) to avoid collisions.

Babiche

Im so sure I called that function once. – Anallise

@cnu he is firing it once, and iOS runtime is firing it once. This event gets called automatically. – Babiche

Thank you , it's OK now!!! I change "UIApplicationWillEnterForegroundNotification" to an other word . – Anallise

Instead of changing it to another word...why not just take out that code, and use the event that comes automatically? – Babiche

His name is borrrden, not OLO. – Chloral

I have the same issue, no double registration with the samen name, 100% sure. The only solution is to post notification with a unique name in AppDelegate's applicationWillEnterForeground or applicationDidBecomeActive. – Airway

"After calling this method, the app also posts a UIApplicationDidBecomeActiveNotification notification to give interested objects a chance to respond to the transition." according to Apple. Well I get 2 notifications after each other. – Airway