REST API client

Question

I am new in iOS development and Swift. I am going to develop a simple application which communicates with external REST services. This is my first experiment.

I appreciate feedback on best practices and improvements. Style comments are always considered as well.

import Foundation
import SwiftyJSON

class UserObject {
    var pictureURL: String!
    var username: String!

    required init(json: JSON) {
        pictureURL = json["picture"]["medium"].stringValue
        username = json["email"].stringValue
    }
}

import Foundation
import SwiftyJSON

typealias ServiceResponse = (JSON, Error?) -> Void

class RestApiManager: NSObject {

    static let sharedInstance = RestApiManager()
    let baseURL = "http://api.randomuser.me/"

    func getRandomUser(onCompletion: @escaping (JSON) -> Void) {

        let route = baseURL
        makeHTTPGetRequest(path: route, onCompletion: { json, err in
            onCompletion(json as JSON)
        })
    }

    private func makeHTTPGetRequest(path: String, onCompletion: @escaping ServiceResponse) {

        let request = URLRequest(url: URL(string: path)!)
        let session = URLSession.shared

        session.dataTask(with: request) {data, response, err in
            if(err != nil) {
                onCompletion(JSON.null, err)
            } else {
                let jsonData = data
                let json:JSON = JSON(data: jsonData!)
                onCompletion(json, nil)
            }
        }.resume()
    }
}

import UIKit
import SwiftyJSON

class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {

    var tableView: UITableView!
    var items = [UserObject]()

    override func viewWillAppear(_ animated: Bool) {

        let frame:CGRect = CGRect(x: 0, y: 100, width: self.view.frame.width, height: self.view.frame.height - 100)
        self.tableView = UITableView(frame: frame)
        self.tableView.dataSource = self
        self.tableView.delegate = self
        self.view.addSubview(self.tableView)

        let btn = UIButton(frame: CGRect(x: 0, y: 25, width: self.view.frame.width, height: 50))
        btn.backgroundColor = UIColor.cyan
        btn.setTitle("Add new dummy", for: UIControlState.normal)
        btn.addTarget(self, action: #selector(addDummyData), for: UIControlEvents.touchUpInside)
        self.view.addSubview(btn)
    }

    func addDummyData() {
        RestApiManager.sharedInstance.getRandomUser { (json: JSON) in
            if let results = json["results"].array {
                for entry in results {
                    self.items.append(UserObject(json: entry))
                }

                DispatchQueue.main.async {
                    self.tableView.reloadData()
                }
            }
        }
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return self.items.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        var cell = tableView.dequeueReusableCell(withIdentifier: "CELL")

        if cell == nil {
            cell = UITableViewCell(style: UITableViewCellStyle.value1, reuseIdentifier: "CELL")
        }

        let user = self.items[indexPath.row]

        if let url = NSURL(string: user.pictureURL) {
            if let data = NSData(contentsOf: url as URL) {
                cell?.imageView?.image = UIImage(data: data as Data)
            }
        }

        cell!.textLabel?.text = user.username
        return cell!
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

}

Answer 1

This is mostly a clean and well considered design. Some opportunities for improvement which stand out:

Make the baseURL property a parameter of the initialiser for RestApiManager. This will allow you to construct the api class with any URL, which is useful for testing, or initialising from a config file.

class RestApiManager: NSObject {

    static let sharedInstance = RestApiManager(baseURL: "http://api.randomuser.me/")
    let baseURL = "http://api.randomuser.me/"
    init(baseURL: URL) {
        self.baseURL = baseURL
    }

RestApiManager.getRandomUser should return a UserObject instance, instead of a dictionary. The view controller should not need to know the intricacies of parsing the JSON object.

func getRandomUser(onCompletion: @escaping ([UserObject]) -> Void) {

    let route = baseURL
    makeHTTPGetRequest(path: route, onCompletion: { json, err in
        var users = [UserObject]()
        if let results = json["results"].array {
            for entry in results {
                users.append(UserObject(json: entry))
            }
        }
        onCompletion(users)
    })
}

The view controller should not depend on a concrete class. The API class should conform to a protocol, which is the dependency used in the view controller. This allows the view controller to be tested with a mock API.

protocol APIProtocol {
    func getRandomUser(completion: @escaping ([UserObject]) -> Void)
}

class RestApiManager: NSObject, APIProtocol {

    func getRandomUser(onCompletion: @escaping ([UserObject]) -> Void) {

Use dependency inversion to pass in an instance of the api class to the view controller.

class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {

    var api: APIProtocol!

    // ... more code

    func addDummyData() {
        api.getRandomUser { (users: [UserObject]) in
            DispatchQueue.main.async { 
                // Update on main queue to prevent race condition 
                // if multiple requests complete at the same time
                self.users.append(contentsOf: users)
                self.tableView.reloadData()
            }
        }
    }

Usage:

let viewController = // instantiate view controller
viewController.api = RestApiManager.sharedInstance