IBPlugin: Adding additional objects on drag from IB Library

Question

I have a list view class that just like NSCollectionView requires an additional prototype item and a prototype view to be of any use. When dropping an NSCollectionView from the library in Interface Builder those two helper items are automatically created. However I couldn't find a single official Apple document dealing with this use case (describing how its done).

Digging thru the Apple Dev Guides I could however find "ibDidAddToDesignableDocument:".
With the following code I managed to get my auxiliary items created on drop from library:

- (void)ibDidAddToDesignableDocument:(IBDocument *)document {
    [super ibDidAddToDesignableDocument:document];

    NSView *prototypeView = [[[NSView alloc] initWithFrame:NSMakeRect(0.0, 0.0, 300, 65.0)] autorelease];
    DLListViewItem *prototypeViewItem = [[[DLListViewItem alloc] initWithNibName:nil bundle:nil] autorelease];

    [document addObject:prototypeViewItem toParent:nil];
    [document addObject:prototypeView toParent:nil];

    [document connectOutlet:@"view" ofSourceObject:prototypeViewItem toDestinationObject:prototypeView];
    [document connectOutlet:@"listView" ofSourceObject:prototypeViewItem toDestinationObject:self];
    [document connectOutlet:@"prototypeItem" ofSourceObject:self toDestinationObject:prototypeViewItem];
}

However…

…IB adds those aux items for NSCollectionView only on the actual initial drag from the library, not on any other call of "ibDidAddToDesignableDocument:", such as when embedding, copying or duplicating the item. (while my method would, and on all)

This makes me wonder whether Apple actually uses "ibDidAddToDesignableDocument:" for this and if I'm on the right track with this at all.

How does one imitate this properly? I'm having a hard time trying to distinguish between different contexts for "ibDidAddToDesignableDocument:". Anybody successfully done this?
Unfortunately none of Google, Google Code, GitHub, or the documentation revealed anything helpful, so I'm in desperate need of help here. :(

Thanks in advance!

Edit: Oh great, this question just brought me the tumbleweed badge, yay! Not.
I'm more into useful answers actually, but thanks anyway ;)

Answer 1

I struggled with this on a plugin I did myself a while ago. In my case I was able to check a property of the object to see if it had been initialized already and skip adding the auxilliary objects in that case. I believe BWToolkit uses some internal checking that is similar. Couldn't you check your object's 'prototypeItem' property to see if you need to skip creating your aux objects?