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. } }

Luke Van In · Accepted Answer · 2017-04-15 12:40:53Z

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

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