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How to load and save a struct in UserDefaults using Codable

Paul Hudson       @twostraws

The Codable protocol makes it easy to load and save native Swift types to JSON, and with a little typecasting you can get that data into UserDefaults so it’s safe.

Here’s some trivial Codable data we can work with:

struct Person: Codable {
    var name: String
}

let taylor = Person(name: "Taylor Swift")

To save that to UserDefaults you must first encode it as JSON using JSONEncoder, which will send back a Data instance you can send straight to UserDefaults. For example:

let encoder = JSONEncoder()
if let encoded = try? encoder.encode(taylor) {
    let defaults = UserDefaults.standard
    defaults.set(encoded, forKey: "SavedPerson")
}

Reading saved data back into a Person instance is a matter of converting from Data using a JSONDecoder, like this:

if let savedPerson = defaults.object(forKey: "SavedPerson") as? Data {
    let decoder = JSONDecoder()
    if let loadedPerson = try? decoder.decode(Person.self, from: savedPerson) {
        print(loadedPerson.name)
    }
}

Available from iOS 8.0 – learn more in my book Swift Design Patterns

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