14、Core Data: Validation, Relationships, and Fetched Properties

Core Data: Validation, Relationships, and Fetched Properties

1. Core Data Validation Error Handling

When running an app and adding a new hero, if you enter edit mode, clear the Name field, and then tap the Identity field, a validation alert dialog will appear. However, it may not display the proper failure reason.

The validate method in the relevant code populates the message like this:

message = NSLocalizedString("Validation error on \(errorKey)\rFailure Reason: \(reason)",
                   comment: "Validation error on \(errorKey)\rFailure Reason: \(reason)")

But the call to error?.localizedFailureReason returns nil because, prior to iOS 4, Core