Question

In my app I have a button, when the user clicks it, it brings up a modal view controller which gets the user’s location (with a UIActivityIndicator and image on). When it has there location it will send them off to another application.

This works well on older devices (without multi-tasking) because the app simply re-launches back to it’s previous state after I go back to it.

However on devices that have multi-tasking, when I resume the app, the view that tells the user it’s getting their location is still there – which is not at all desired.

My first idea was to set a BOOL when it was about to fire them off to the other app, and then in the viewDidAppear, if the BOOL is true, dismiss the modal view.

That would work, if viewDidAppear got called when an app resumes active. As I have just learnt, it doesn’t.

Is there a method that view controllers can respond to when the app resumes active to that view? Or, will I have to set up delegation etc with the app delegate? If so, can you explain how I would do that?

Answer 1

You can send a notification when the app becomes active and listen to it into your modalviewcontroller. I think this is the easiest way.

// Into the app delegate
- (void)applicationDidBecomeActive:(UIApplication *)application
{
    [[NSNotificationCenter defaultCenter] postNotificationName:@"ApplicationDidBecomeActive" object:nil];
}

// Into your modal view controller register it for the given notification
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationDidBecomeActive:) name:@"ApplicationDidBecomeActive" object:nil];

- (void)applicationDidBecomeActive:(NSNotification *)notification
{
//...
}

Otherwise you can disable the background mode of your application by setting the “UIApplicationExitsOnSuspend” key to YES in the info.plist file.