Core Data in Objective-C, 3rd Edition

The DocumentPreferences Object

To build a system that imitates the NSUserDefaults, we need to have a single object that manages the parameters table for us. By doing so, we can treat the entire parameters table as if it were a single object with a dynamic number of accessors. However, we don’t want to have to write an accessor every time that we add a parameter; ideally, we want to just call ‑valueForKey: and ‑setValue:forKey: and not worry about the persistence of these values. Lastly, we want to be able to set up some default values.

An important point about the defaults is that they aren’t persisted to disk. If they get persisted, then later versions that change the default would require additional code to check for persisted defaults and ...