-applicationDidFinishLaunching: will be sent to the application delegate as described above. However, it is a notification as well. NSApplication sends the notification NSApplicationDidFinishLaunchingNotification. The application’s delegate is automatically registered for this notification if it implements -applicationDidFinishLaunching:. But any object can register for that notification.

In general, most delegate methods in Cocoa that have Will or Did in their names are convenience covers for notifications. (The definitive way to tell is in the delegate method takes a single (NSNotification*) parameter.) For all these methods, there’s a corresponding string constant for the notification name and any object can register to receive those notifications with NSNotificationCenter. Multiple objects can receive any notification.

Of course, to usefully register an object to receive the NSApplicationDidFinishLaunchingNotification, you must do it early enough to know that that notification has not already been sent…

Someone asked who sends these messages.

-awakeFromNib is sent by the nib loading machinery (which is implemented as a category addition to NSBundle in AppKit. It’s declared in AppKit/NSNibLoading.h) -[NSBundle loadNibFile:externalNameTable:withZone:], specifically, will load the nib, get it all set up and connected, and invoke -awakeFromNib on all relevant objects.

-applicationDidFinishLaunching: is invoked indirectly by NSNotificationCenter. NSApplication posts the notification.

Rainer,

Thank you for the tip on application load. I never put those two together before but now that you have for me it makes perfect sense.

Paul,

Yes I could have written that part better. Hopefully with the addition of the new image it will be easier to understand.

Granted, I think that icon is new in IB3.0, so possibly you mean that the File’s owner is set to NSApplication, but then I don’t see how ‘In this [second] example you can see the reference to the NSApplication in the nib’

Could you explain a bit more?

Second important call in the app delegate is applicationWillFinishLaunching, which will be called earlier; in fact, while the icon is still bouncing in the Dock (applicationDidFinishLaunching is called when the icon stops bouncing). So this is a place to early-initialize application stuff.

If your app is opened by double-clicking on a document icon, application:openFile: will be called on the app delegate before applicationWillFinishLaunching is called. So if you implement that method too, you should do something like [self performSelector:... withObject:filename afterDelay:0.0] to act on the file after the run loop gets going.

Finally, the main run loop is started after applicationWillFinishLaunching returns.

I am probably being a bit thick (fairly new to Mac development), but where should I see this reference to NSApplication? I thought you meant the icon labelled Application, but that’s in both examples. Do you mean the MainMenu instead? Sorry if I’m asking a dumb question here.

You can use this knowledge to influence the “perceived” launch time of your application, by segregating heavy initialization code into the latter method where it makes sense, reducing the number of launch-time Dock bounces.

By the way, Marcus and Matt, the blog is a great read. Keep the technical stuff coming!

As for the awakeFromNib it can vary greatly but on startup it is generally the NSApplication also. Later in the applications life it is usually you :)