Question

For my current app I’m using the NSKeyedArchiver approach to persist my objects to the iPhone between launches. I’m wondering if it makes sense to tag this file when it’s created with a version number so that in the future when the app revs we’ll know what kind of data we’re dealing with should migration be necessary. Is this recommended for something as simple as an NSArray of custom objects that are serialized with NSKeyedArchiver? If so how/where to stash the version number?

Thanks!

Answer 1

If you feel like the format will change, then yes, you’ll want some way to detect which version of the file you’re working with. A simple way to do this (since you’re using NSArray) would be to simply add the version number as an NSNumber to either the beginning or end of the array. Alternatively, for a more complicated approach that doesn’t actually change the files, you could store the information in a separate file (say, using an NSDictionary that links the file name and version number). Or, you could use the user defaults system to store it, and if it’s frome an older version, update the file and the user defaults key.

I wouldn’t use the second method, unless you’re dealing with multiple keyed data files. Of those three, I’d probably choose the last, but there may be some other way to do it that makes more sense.