Unbox | Wrap
Unbox is an easy to use Swift JSON decoder. Don't spend hours writing JSON decoding code - just unbox it instead!
Unbox is lightweight, non-magical and doesn't require you to subclass, make your JSON conform to a specific schema or completely change the way you write model code. It can be used on any model with ease.
Say you have your usual-suspect User model:
struct User {
let name: String
let age: Int
}That can be initialized with the following JSON:
{
"name": "John",
"age": 27
}To decode this JSON into a User instance, all you have to do is make User conform to Unboxable and unbox its properties:
struct User {
let name: String
let age: Int
}
extension User: Unboxable {
init(unboxer: Unboxer) throws {
self.name = try unboxer.unbox(key: "name")
self.age = try unboxer.unbox(key: "age")
}
}Unbox automatically (or, actually, Swift does) figures out what types your properties are, and decodes them accordingly. Now, we can decode a User like this:
let user: User = try unbox(dictionary: dictionary)or even:
let user: User = try unbox(data: data)The first was a pretty simple example, but Unbox can decode even the most complicated JSON structures for you, with both required and optional values, all without any extra code on your part:
struct SpaceShip {
let type: SpaceShipType
let weight: Double
let engine: Engine
let passengers: [Astronaut]
let launchLiveStreamURL: URL?
let lastPilot: Astronaut?
let lastLaunchDate: Date?
}
extension SpaceShip: Unboxable {
init(unboxer: Unboxer) throws {
self.type = try unboxer.unbox(key: "type")
self.weight = try unboxer.unbox(key: "weight")
self.engine = try unboxer.unbox(key: "engine")
self.passengers = try unboxer.unbox(key: "passengers")
self.launchLiveStreamURL = unboxer.unbox(key: "liveStreamURL")
self.lastPilot = unboxer.unbox(key: "lastPilot")
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "YYYY-MM-dd"
self.lastLaunchDate = unboxer.unbox(key: "lastLaunchDate", formatter: dateFormatter)
}
}
enum SpaceShipType: Int, UnboxableEnum {
case apollo
case sputnik
}
struct Engine {
let manufacturer: String
let fuelConsumption: Float
}
extension Engine: Unboxable {
init(unboxer: Unboxer) throws {
self.manufacturer = try unboxer.unbox(key: "manufacturer")
self.fuelConsumption = try unboxer.unbox(key: "fuelConsumption")
}
}
struct Astronaut {
let name: String
}
extension Astronaut: Unboxable {
init(unboxer: Unboxer) throws {
self.name = try unboxer.unbox(key: "name")
}
}Decoding JSON is inherently a failable operation. The JSON might be in an unexpected format, or a required value might be missing. Thankfully, Unbox takes care of handling both missing and mismatched values gracefully, and uses Swift’s do, try, catch pattern to return errors to you.
You don’t have to deal with multiple error types and perform any checking yourself, and you always have the option to manually exit an unboxing process by throwing. All errors returned by Unbox are of the type UnboxError.
Unbox supports decoding all standard JSON types, like:
BoolInt,Double,FloatStringArrayDictionary
It also supports all possible combinations of nested arrays & dictionaries. As you can see in the Advanced example above (where an array of the unboxable Astronaut struct is being unboxed), we can unbox even a complicated data structure with one simple call to unbox().
Finally, it also supports URL through the use of a transformer, and Date by using any DateFormatter.
Unbox also supports transformations that let you treat any value or object as if it was a raw JSON type.
It ships with a default String -> URL transformation, which lets you unbox any URL property from a string describing an URL without writing any transformation code.
The same is also true for String -> Int, Double, Float, CGFloat transformations. If you’re unboxing a number type and a string was found, that string will automatically be converted to that number type (if possible).
To enable your own types to be unboxable using a transformation, all you have to do is make your type conform to UnboxableByTransform and implement its protocol methods.
Here’s an example that makes a native Swift UniqueIdentifier type unboxable using a transformation:
struct UniqueIdentifier: UnboxableByTransform {
typealias UnboxRawValueType = String
let identifierString: String
init?(identifierString: String) {
if let UUID = NSUUID(uuidString: identifierString) {
self.identifierString = UUID.uuidString
} else {
return nil
}
}
static func transform(unboxedValue: String) -> UniqueIdentifier? {
return UniqueIdentifier(identifierString: unboxedValue)
}
}No matter if the root object of the JSON that you want to unbox is an Array or Dictionary - you can use the same Unbox() function and Unbox will return either a single model or an array of models (based on type inference).
You can also unbox enums directly, without having to handle the case if they failed to initialize. All you have to do is make any enum type you wish to unbox conform to UnboxableEnum, like this:
enum Profession: Int, UnboxableEnum {
case developer
case astronaut
}Now Profession can be unboxed directly in any model
struct Passenger: Unboxable {
let profession: Profession
init(unboxer: Unboxer) throws {
self.profession = try unboxer.unbox(key: "profession")
}
}Sometimes you need to use data other than what's contained in a dictionary during the decoding process. For this, Unbox has support for strongly typed contextual objects that can be made available in the unboxing initializer.
To use contextual objects, make your type conform to UnboxableWithContext, which can then be unboxed using unbox(dictionary:context) where context is of the type of your choice.
You can also use key paths (for both dictionary keys and array indexes) to unbox values from nested JSON structures. Let's expand our User model:
{
"name": "John",
"age": 27,
"activities": {
"running": {
"distance": 300
}
},
"devices": [
"Macbook Pro",
"iPhone",
"iPad"
]
}struct User {
let name: String
let age: Int
let runningDistance: Int
let primaryDeviceName: String
}
extension User: Unboxable {
init(unboxer: Unboxer) throws {
self.name = try unboxer.unbox(key: "name")
self.age = try unboxer.unbox(key: "age")
self.runningDistance = try unboxer.unbox(keyPath: "activities.running.distance")
self.primaryDeviceName = try unboxer.unbox(keyPath: "devices.0")
}
}You can also use key paths to directly unbox nested JSON structures. This is useful when you only need to extract a specific object (or objects) out of the JSON body.
{
"company": {
"name": "Spotify",
},
"jobOpenings": [
{
"title": "Swift Developer",
"salary": 120000
},
{
"title": "UI Designer",
"salary": 100000
},
]
}struct JobOpening {
let title: String
let salary: Int
}
extension JobOpening: Unboxable {
init(unboxer: Unboxer) throws {
self.title = try unboxer.unbox(key: "title")
self.salary = try unboxer.unbox(key: "salary")
}
}
struct Company {
let name: String
}
extension Company: Unboxable {
init(unboxer: Unboxer) throws {
self.name = try unboxer.unbox(key: "name")
}
}let company: Company = try unbox(dictionary: json, atKey: "company")
let jobOpenings: [JobOpening] = try unbox(dictionary: json, atKey: "jobOpenings")
let featuredOpening: JobOpening = try unbox(dictionary: json, atKeyPath: "jobOpenings.0")Sometimes you need more fine grained control over the decoding process, and even though Unbox was designed for simplicity, it also features a powerful custom unboxing API that enables you to take control of how an object gets unboxed. This comes very much in handy when using Unbox together with Core Data, when using dependency injection, or when aggregating data from multiple sources. Here's an example:
let dependency = DependencyManager.loadDependency()
let model: Model = try Unboxer.performCustomUnboxing(dictionary: dictionary, closure: { unboxer in
var model = Model(dependency: dependency)
model.name = unboxer.unbox(key: "name")
model.count = unboxer.unbox(key: "count")
return model
})CocoaPods:
Add the line pod "Unbox" to your Podfile
Carthage:
Add the line github "johnsundell/unbox" to your Cartfile
Manual:
Clone the repo and drag the file Unbox.swift into your Xcode project.
Swift Package Manager:
Add the line .Package(url: "https://github.com/johnsundell/unbox.git", majorVersion: 2) to your Package.swift
Unbox supports all current Apple platforms with the following minimum versions:
- iOS 8
- OS X 10.11
- watchOS 2
- tvOS 9
In case your unboxing code isn’t working like you expect it to, here are some tips on how to debug it:
Compile time error: Ambiguous reference to member 'unbox'
Swift cannot find the appropriate overload of the unbox method to call. Make sure you have conformed to any required protocol (such as Unboxable, UnboxableEnum, etc). Note that you can only conform to one Unbox protocol for each type (that is, a type cannot be both an UnboxableEnum and UnboxableByTransform). Also remember that you can only reference concrete types (not Protocol types) in order for Swift to be able to select what overload to use.
unbox() throws
Use the do, try, catch pattern to catch and handle the error:
do {
let model: Model = try unbox(data: data)
} catch {
print("An error occured: \(error)")
}If you need any help in resolving any problems that you might encounter while using Unbox, feel free to open an Issue.
- UnboxedAlamofire - the easiest way to use Unbox with Alamofire
For more updates on Unbox, and my other open source projects, follow me on Twitter: @johnsundell
Also make sure to check out Wrap that let’s you easily encode JSON.