A lightweight property wrapper for UserDefaults done right

Read the post: A better approach to writing a UserDefaults Property Wrapper

Foil, as in "let me quickly and easily wrap and store this leftover food in some foil so I can eat it later." 🌯 😉

Foil:
noun
North America
A very thin, pliable, easily torn sheet of aluminum used for cooking, packaging, cosmetics, and insulation.

You can use @WrappedDefault for non-optional values and @WrappedDefaultOptional for optional ones. You may wish to store all your user defaults in one place, however, that is not necessary. Any property on any type can use this wrapper.

final class AppSettings {
    static let shared = AppSettings()

    @WrappedDefault(key: "flagEnabled")
    var flagEnabled = true

    @WrappedDefault(key: "totalCount")
    var totalCount = 0

    @WrappedDefaultOptional(key: "timestamp")
    var timestamp: Date?
}

// Usage

func userDidToggleSetting(_ sender: UISwitch) {
    AppSettings.shared.flagEnabled = sender.isOn
}

There is also an included example app project.

If you prefer using an enum for the keys, writing an extension specific to your app is easy. However, this is not required. In fact, unless you have a specific reason to reference the keys, this is completely unnecessary.

enum AppSettingsKey: String, CaseIterable {
    case flagEnabled
    case totalCount
    case timestamp
}

extension WrappedDefault {
    init(wrappedValue: T, _ key: AppSettingsKey) {
        self.init(wrappedValue: wrappedValue, key: key.rawValue)
    }
}

extension WrappedDefaultOptional {
    init(_ key: AppSettingsKey) {
        self.init(key: key.rawValue)
    }
}

There are many ways to observe property changes. The most common are by using Key-Value Observing or a Combine Publisher. KVO observing requires the object with the property to inherit from NSObject and the property must be declared as @objc dynamic.

final class AppSettings: NSObject {
    static let shared = AppSettings()

    @WrappedDefaultOptional(key: "userId")
    @objc dynamic var userId: String?

    @WrappedDefaultOptional(key: "average")
    var average: Double?
}

let observer = AppSettings.shared.observe(\.userId, options: [.new]) { settings, change in
    print(change)
}

Note: that average does not need the @objc dynamic annotation, .receiveValue will fire immediately with the current value of average and on every change after.

AppSettings.shared.$average
    .sink {
        print($0)
    }
    .store(in: &cancellable)

Note: in this case, userId needs the @objc dynamic annotation and AppSettings needs to inherit from NSObject. Then receiveValue will fire only on changes to wrapped object's value. It will not publish the initial value as in the example above.

AppSettings.shared
    .publisher(for: \.userId, options: [.new])
    .sink {
        print($0)
    }
    .store(in: &cancellable)

The following types are supported by default for use with @WrappedDefault.

Adding support for custom types is possible by conforming to UserDefaultsSerializable. However, this is highly discouraged. UserDefaults is not intended for storing complex data structures and object graphs. You should probably be using a proper database (or serializing to disk via Codable) instead.

• Bool
• Int
• UInt
• Float
• Double
• String
• URL
• Date
• Data
• Array
• Set
• Dictionary
• RawRepresentable types

• NSUserDefaults in Practice, the excellent guide by David Smith
• UserDefaults documentation
• Preferences and Settings Programming Guide
• Property List Programming Guide

• iOS 13.0+
• tvOS 13.0+
• watchOS 6.0+
• macOS 11+

• Swift 5.5+
• Xcode 13.0+
• SwiftLint

pod 'Foil', '~> 3.0.0'

dependencies: [
    .package(url: "https://github.com/jessesquires/Foil.git", from: "3.0.0")
]

Alternatively, you can add the package directly via Xcode.

You can read the documentation here. Generated with jazzy. Hosted by GitHub Pages.

Interested in making contributions to this project? Please review the guides below.

• Contributing Guidelines
• Code of Conduct
• Support and Help
• Security Policy

Also consider sponsoring this project or buying my apps! ✌️

Created and maintained by Jesse Squires.

Released under the MIT License. See LICENSE for details.

Copyright © 2021-present Jesse Squires.