CODEWITHSUNDEEP
iosobjective-c
rihekopo
rihekopo

Reputation: 3350

Dealing with the same NSNotification in multiple view controllers

I'm using the below notifications to reload ViewControllerA when my app comes back from background mode. It works correctly, but the applicationEnteredForeground: method gets called every time when I open the app again. For example if I close the app when ViewControllerB or ViewControllerC is on the screen and open it again the method will be called despite the viewDidLoad of ViewControllerB doesn't contain applicationEnteredForeground: method. I would like to know that how could solve this issue? My goal is to use applicationEnteredForeground: only when ViewControllerA was on the screen before I closed the app. As a possible solution I would just remove the NSNotificationCenter in the viewDidDisappear, but since the observer is in the viewDidLoad it won't work when the user navigates back, because viewDidLoad won't be called again. Is there any fix for this? 

- (void)viewDidLoad {

   [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(applicationEnteredForeground:)
                                                 name:UIApplicationWillEnterForegroundNotification
                                               object:nil];

}

- (void)applicationEnteredForeground:(NSNotification *)notification {

  // do stuff...

}

Upvotes: 0

Views: 587

Answers (2)

deadbeef
deadbeef

Reputation: 5563

You can check if a view controller is on screen by checking the window property of it's view. It will work in most standard cases.

- (void)applicationEnteredForeground:(NSNotification *)notification
{
    if (self.view.window == nil) {
        // Not on screen
        return;
    }

    // do stuff...
}

Upvotes: 1

Joshua Sullivan
Joshua Sullivan

Reputation: 1139

You should remove ViewController A's event listener on viewWillDisappear and add it in viewWillAppear. That way, VC A will only be listening when it is the visible view controller.

Upvotes: 2

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