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

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;
}