Heys, I am writing something in Xcode. I use Core Data for persistency and link the view and the model together with Cocoa Bindings; pretty much your ordinary Core Data application. I have an array controller (NSArrayController) in my Xib. This has its managedObjectContext bound to the AppDelegate, as is convention, and tracks an entity. So far so good. Now, the "Content Set" biding of this NSArrayController limits its content set (as you'd expect), by a keyPath from the selection in another NSArrayController (otherAc.selection.detailsOfMaster). This is the usual way to implement a Master-Detail relationship. I want to variably change the key path at runtime, using other controls. This way, I sould return a content set that includes several other content sets, which is all advanced and beyond Interface Builder. To achieve this, I think I should bind the Content Set to my AppDelegate instead. I have tried to do this, but don't know what methods to implement. If I just create the KVC methods (objectSet, setObjectSet), then I can provide a Content Set for the Array Controller in the contentSet method. However, I don't think I'm binding this properly, because it doesn't "refresh". I'm new to binding; what do I need to implement to properly update the Content Set when other things, like the selection in the master NSArrayController, changes?