How do I use a subclass of NSDocumentController in XCode 4?

Question

I am currently in the process of trying to teach myself Cocoa development. Toward this end, I purchased a mostly-excellent book, Cocoa Recipes for Mac OS X: Vermont Recipes, which walks through creating a sample application. It's pretty good, but it's written against XCode 3.2 rather than XCode 4. So far, I've been able to bridge this myself, but I've run up against an issue where I can't figure out how to follow the instruction.

Essentially, the book goes through a sample case of subclassing NSDocumentController so that the application can handle two (eventually maybe an arbitrary number) different types of documents, and so it opens the appropriate window for each type. So, I've created a custom subclass of NSDocumentController (which the book calls VRDocumentController), and now I need to make it such that an instance of this controller loads relatively early in the application launch process. Basically, the class is a singleton, and so I have to instantiate mine before the application instantiates the standard class, and this has to be done early in the process. Fair enough.

The book cites the Apple documentation for subclassing NSDocumentController, which states that there are two ways to attack the problem: to instantiate the class in your MainMenu.xib file or to instantiate one in your -applicationWillFinishLaunching: delegate method. The Apple documentation doesm't give clear instruction on how to do either of these (more on that in a moment) and the book covers only the first version, which I think is probably my preferred method.

My problem: I cannot for the life of me pull this off in XCode 4. The instructions the book provides for XCode 3.2 are no longer accurate, because Interface Builder has been shuffled into XCode itself now and the new version of the "classes tab" no longer shows my project's classes. I found this question on Stack Overflow asking a similar question, so I tried following the accepted answer there. However, when I open the Identity Inspector and try to type VRDocumentController, it just beeps at me and doesn't take it. None of the other controller classes I've written seem to be acceptable inputs either.

I'd also be happy to go the other route; instantiating a copy in the -applicationWillFinishLaunching method. But, I have no earthly idea in which class that method actually belongs, or what its return type is. I've done a non-trivial amount of searching for that, too, with no luck.

Answer 1

Just create an object in the main storyboard, set it's class as your NSDocumentController subclass, and it will be used as the application shared document controller.

Answer 2

Easier method of getting the Custom Document Controller created in time is to implement the + (void) load method:

This is literally all you need to do it implement a custom document controller.

@implementation AppDocumentController

+ (void) load
{
    [AppDocumentController new];
}

// ... your overriding goes here

@end

This is cool because there's no separation of the codez. Not 100% sure if the controller is created too early, but works well for me.