[iOS]: detect when view controller appears after back from another external app

Question

This is my escenario:

I have a view controller where the user can go to another application (Settings) when push a button in this way:

    -(void) goToSettings{
       [[UIApplication sharedApplication] openURL:[NSURL URLWithString:UIApplicationOpenSettingsURLString]];
    }

So, this code open the app's screen settings and it shows in the upper left corner a legend like this:

Back to myApplication

I wish to detect when the view controller where user push the button is active again. I know you can detect when app is active again with this method in the delegate file

- (void)applicationWillEnterForeground:(UIApplication *)application

But I need detect in specific the view controller. I have tried with -(void)viewWillAppear:(BOOL)animated but It not works. Anyone have any idea about this?

Answer 1

Setup your view controller to listen for the UIApplicationDidBecomeActiveNotification notification.

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

Then add the becomeActive: method:

- (void)becomeActive:(NSNotification *)notification {
    // App is active again - do something useful
}

And be sure to remove the observer at the appropriate point.

[[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidBecomeActiveNotification object:nil];

Of course your app may become active again for lots of reasons, not just returning from the Settings app.