问题

I have the following models in my application.

Board, holds a NSMutableArray property lists of type List below
List, holds a NSArray property cards of type Card below
Card, has a NSString property name

The relationship is thus Board --> to-many List --> to-many Card

I have a NSCollectionView based master-detail interface, where I want to display Boards in the master and its corresponding Lists+Cards in the detail view.

The master interface is fine, the elements Board are displayed nicely.

Bindings are setup like so:

BoardArrayController -> bound to File's owner

** Model key path: boards
** Mode: Class
** Item prototype: Board View Item

ListArrayController -> bound to BoardArrayController.

** Controller key: ~~arrangedObjects~~ selection
** Model key path: lists
** Mode: Class
** Item prototype: List View Item

CardArrayController -> bound to ListArrayController

** Controller key: ~~arrangedObjects~~ selection
** Model key path: cards
** Mode: Class

The master collection view has the Content bound to BoardArrayController

** Controller key: arrangedObjects

The detail collection view has the Content bound to the BoardArrayController

** Controller key: selection
** Model key path: lists

View item prototype

Any view element in the prototype views (those that are added with the NSCollectionView) have the following info

** Bound to: Board View Item (master) or List View Item (detail)
** Model key path: representedObject followed by .property

Problem

The detail interface is not updated when I click a board in the master view. I expect a new set of lists+cards being displayed. It is only the one loaded at startup which is being displayed.

Questions

Is this a NSCollectionView selection problem or a binding problem?

Hint: I think it's a binding problem. Because it works, if in my controller I observe masterView.selectionIndexes and bind an IBOutlet to detailedView. Then in observeValueForKeyPath:ofObject:change:context: I manually call detailedView:setContent:.

Edit: updated setup description in accordance to the answer in Cocoa Bindings for hierarchical model