Question

Using this guide I have created a static library (let’s call it AppCore) that can be shared between the Mac OS X and iOS versions of one app. This static library uses Core Data and the point of it is to share the model part and schema versioning between different implementations.

I created a NSPersistentDocument based project that will depend on this AppCore. In this project I added a reference to the .xcdatamodel file. Then I created a simple table view with add/remove buttons to edit an array of one entity type with the assisted “new core data entity” item. This created an instance of NSArrayController and the required bindings for the add/remove behaviour.

Now, everything seems to work fine when I’m using the default class for the Core Data entities (NSManagedObject) and I’m able to add new rows using the +/- buttons. However, when I change the entity implementation class to a custom one, I’m getting an error

Failed to create new object

This seems to come from the NSArrayController and it seems to be unable to instantiate the required entity. I can, however, create one in the NSPersistentDocument subclass by:

[NSEntityDescription insertNewObjectForEntityForName:@"SomeEntity" inManagedObjectContext:[self managedObjectContext]]

What confuses me is why the instance of NSArrayController can’t. If I understand correctly, the array controller is instructed to create an entity, not class and my guess is that the entities are created with the help of NSEntityDescription class. I could implement my own version of the array controller’s add: but then again, it might be that here something is fundamentally wrong. I haven’t touched the init:s and the custom entity class implementation is simply for convenience, to access the attributes directly.

I have tried changing the base SDK on the AppCore but without effect. Currently it uses the iOS version but I’m not sure how it should be. This is another question but if unrelated, I might ask it here on a separate question.

So, to summarize, why can’t the NSArrayController create an instance of this entity?

Thanks in advance.

Update

This works if I add the SomeEntity class from the AppCore to the dependent project as a reference. This is not the most usable way since modifications to the AppCore has to be propagated to the dependatnt projects also.

Answer 1

Bingo. I missed the “-ObjC” flag for the dependant project’s “other linker flags”. Now everything works like a charm.