Call function when Notification Center is dismissed

Question

I am just coding my first iOS app using a today widget (using Swift). I was wondering if there is a function that is called whenever my app comes back to the foreground after dismissing the notification center.

I know I can use an Observer to check for UIApplicationWillEnterForegroundNotification but my function does not get called when pulling down the notification center while using my app and dismissing it again.

My problem is simple: It is quite unlikely users will pull down the notification center to manipulate data I am using in the app, but I still have to consider what happens if they do. The user is supposed to be able to save his current location by pressing the today widget button.

If that happens while using my app, the app won't check for new data.

Answer 1

I used the following code for determining if the notification center was opened during the application's run time:

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController
{
    BOOL notificationCenterCurrentlyDisplayed;
}

- (void) viewDidLoad
{
    [super viewDidLoad];
    notificationCenterCurrentlyDisplayed = false;
    NSNotificationCenter *defaultCenter = [NSNotificationCenter defaultCenter];
    [defaultCenter addObserver:self selector:@selector(onNotificationCenterDisplayed) name:UIApplicationWillResignActiveNotification object:nil];
    [defaultCenter addObserver:self selector:@selector(onNotificationCenterDismissed) name:UIApplicationDidBecomeActiveNotification object:nil];
}

- (void) onNotificationCenterDisplayed
{
    notificationCenterCurrentlyDisplayed = true;
    NSLog(@"Notification center has been displayed!");
}

- (void) onNotificationCenterDismissed
{
    // Reason for this check is because once the app is launched the UIApplucationDidBecomeActiveNotification is called.
    if (notificationCenterCurrentlyDisplayed)
    {
        notificationCenterCurrentlyDisplayed = false;
        NSLog(@"Notification center has been dismissed!");
    }
}
@end

Also the notification center was displayed method will also be called when the user decides to close the application into the background.