Tips on how to parse JSON in Swift utilizing Codable protocol?

Dependencies

To start with just some phrases about dependencies. From Swift 4 you don’t want any dependency to parse JSON knowledge, as a result of there are built-in protocols to maintain every thing. In case you are nonetheless utilizing some sort of Third-party you must positively ditch it for the sake of simplicity. By the way in which earlier than you add any exterior dependency into your undertaking, please assume twice. 🤔

Networking

In case your job is just to load some sort of JSON doc by way of HTTP from across the internet, – shock – you gained’t want Alamofire in any respect. You need to use the built-in URLSession class to make the request, and get again every thing that you just’ll want. The Basis networking stack is already a posh and really helpful stack, don’t make issues much more sophisticated with further layers.

JSON parsing

Now, after the brief intro, let’s dive in and get some actual faux JSON knowledge from the JSONPlaceholder internet service. I’m going to put the entire thing proper right here, you possibly can choose it, copy and paste right into a Swift playground file.

import Basis
import PlaygroundSupport

PlaygroundPage.present.needsIndefiniteExecution = true

struct Submit: Codable {

    enum CodingKeys: String, CodingKey {
        case id
        case title
        case physique
        case userIdentifier = "userId"
    }

    let id: Int
    let title: String
    let physique: String
    let userIdentifier: Int
}

let url = URL(string: "https://jsonplaceholder.typicode.com/posts")!

URLSession.shared.dataTask(with: url) { knowledge, response, error in
    if let error = error {
        print("Error: (error.localizedDescription)")
        PlaygroundPage.present.finishExecution()
    }
    guard 
        let httpResponse = response as? HTTPURLResponse, 
        httpResponse.statusCode == 200 
    else {
        print("Error: invalid HTTP response code")
        PlaygroundPage.present.finishExecution()
    }
    guard let knowledge = knowledge else {
        print("Error: lacking knowledge")
        PlaygroundPage.present.finishExecution()
    }

    // be at liberty to uncomment this for debugging knowledge
    // print(String(knowledge: knowledge, encoding: .utf8))

    do {
        let decoder = JSONDecoder()
        let posts = strive decoder.decode([Post].self, from: knowledge)

        print(posts.map { $0.title })
        PlaygroundPage.present.finishExecution()
    }
    catch {
        print("Error: (error.localizedDescription)")
        PlaygroundPage.present.finishExecution()
    }
}.resume()

As you possibly can see downloading and parsing JSON from the net is a very easy job. This complete code snippet is round 50 strains of code. In fact it’s only a proof of idea, however it works and also you don’t want any dependency. It’s pure Swift and Basis.

NOTE: To save some typing, you may as well generate the ultimate objects instantly from the JSON construction with these wonderful Xcode extensions.

The Codable protocol – which is definitely a compound typealias from Encodable & Decodable protocols – makes the method of parsing JSON knowledge in Swift magical. 💫