1 Reply
      Latest reply on Dec 28, 2016 3:44 PM by eskimo
      logistes Level 1 Level 1 (0 points)



        I am trying to develop a generic way to populate UITabeViewDataSource. It is largely working, but I had a print statement in the init() and it was causing a crash. It was printing entityName, a computed property, coded thusly:


        public class RecordArray<T: NSManagedObject> {
            var entityName: String {
                let entity = T.entity()
                return entity.name!


        When I step through it, entity is all zeroes, like a classical objective-c nil, even though entity() is a non-optional function. But in later functions it works.


        Does anyone know the reason for this?




        • Re: Why is T.entity() returning zeroes in init()?
          eskimo Apple Staff Apple Staff (13,925 points)

          I’ve seen this sort of thing when properties do not have their nullability set correctly.  In this case entity is declared as never being nil, but it sounds like it is.  Alas, the documentation doesn’t shed any light on why this might happen.  I recommend two things:

          1. Confirm that this is, in fact, the problem.  You can do this by adding an Objective-C category that declares a a new property, maybeEntity perhaps, that is optional.  Then have the Objective-C method implementation just return the entity property.  At that point your Swift code can access maybeEntity and determine if it is indeed nil.

          2. Once you’ve confirmed the problem, you might ask over in App Frameworks > Core Data to see if anyone can input as to why it might be happening.

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