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Setting up

This is our fourth technique project, and we're going to go back to project 10 and fix its glaring bug: all the names and faces you add to the app don't get saved, which makes the app rather pointless!

We're going to fix this using a new class called UserDefaults and two new protocols called Codable and NSCoding – both of those protocols are designed to do the same thing, but the former is available only to Swift developers whereas the latter is also available to Objective-C developers.

Along the way you’ll also meet the classes NSKeyedArchiver and NSKeyedUnarchiver (for use with NSCoding), and JSONEncoder and JSONDecoder (for use with Codable), all of which are there to convert custom objects into data that can be written to disk.

Putting all that together, we're going to update project 10 so that it saves its people array whenever anything is changed, then loads when the app runs.

We're going to be modifying project 10 twice over, once for each method of solving the problem, so I suggest you take a copy of the project 10 folder twice – call the copies project12a and project12b.

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