Getting notified when the current application changes in Cocoa

Question

I want to be notified when the current application will change. I looked at NSWorkspace. It will send notifications only when your own application becomes active or loses the activity. I want to be informed about every application. How can I do this in Cocoa?

Answer 1

If you're targeting 10.6 or later there's a notification for this:

// NSWorkspaceDidActivateApplicationNotification
[[[NSWorkspace sharedWorkspace] notificationCenter] addObserver:self selector:@selector(foremostAppActivated:) name:NSWorkspaceDidActivateApplicationNotification object:nil];

Apple docs: http://developer.apple.com/library/mac/DOCUMENTATION/Cocoa/Reference/ApplicationKit/Classes/NSWorkspace_Class/Reference/Reference.html#//apple_ref/doc/uid/20000391-SW97

Answer 2

Thank you Jason. kEventAppFrontSwitched in Carbon Event Manager is the magic word

- (void) setupAppFrontSwitchedHandler
{
    EventTypeSpec spec = { kEventClassApplication,  kEventAppFrontSwitched };
    OSStatus err = InstallApplicationEventHandler(NewEventHandlerUPP(AppFrontSwitchedHandler), 1, &spec, (void*)self, NULL);

    if (err)
        NSLog(@"Could not install event handler");
}

- (void) appFrontSwitched {
    NSLog(@"%@", [[NSWorkspace sharedWorkspace] activeApplication]);
}

And the handler

static OSStatus AppFrontSwitchedHandler(EventHandlerCallRef inHandlerCallRef, EventRef inEvent, void *inUserData)
{
    [(id)inUserData appFrontSwitched];
    return 0;
}