un-react-example.swift

import UIKit
import PlaygroundSupport

let cellIdentifier = "cellId"
let dataUrl = URL(string: "https://raw.githubusercontent.com/facebook/react-native/master/docs/MoviesExample.json")!

func contstraint(_ attr: NSLayoutAttribute, from: UIView, to: UIView) -> NSLayoutConstraint {
    return NSLayoutConstraint(
        item: from,
        attribute: attr,
        relatedBy: .equal,
        toItem: to,
        attribute: attr,
        multiplier: 1,
        constant: 1
    )
}

struct Movie {
    let title: String
    let thumbnail: URL
    init?(json: [String : Any]) {
        guard let title = json["title"] as? String,
              let images = json["posters"] as? [String : String],
              let tumbnailURLString = images["thumbnail"],
              let thumbnailURL = URL(string: tumbnailURLString)
        else {
            return nil
        }
        self.title = title
        self.thumbnail = thumbnailURL
    }
}

func loadMovies(completionHandler: @escaping ([Movie]) -> Void) {
    let task = URLSession(configuration: .default).dataTask(with: dataUrl) { (data, response, error) in
        if let data = data {
            do {
                if let json = try JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [String : Any],
                   let movies = json["movies"] as? [[String : Any]]
                {
                    completionHandler(movies.flatMap { Movie(json: $0) })
                }
            } catch {}
        }
    }
    task.resume()
}

extension UIImageView {
    func loadImage(url: URL, placeholder: String) {
        image = UIImage(named: placeholder)
        _ = URLSession(configuration: .default).dataTask(with: url) { [weak self] (data, response, error) in
            if let data = data, let img = UIImage(data: data) {
                DispatchQueue.main.async {
                    self?.image = img
                }
            } else if let err = error {
                print("Error: \(url) \(err)")
            } else {
                print("Error: \(url)")
            }
        }.resume()
    }
}

class MovieCell: UITableViewCell {
    init() {
        super.init(style: .default, reuseIdentifier: cellIdentifier)
    }
    
    required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") }
}

class MoviesListViewController: UITableViewController {
    var data: [Movie]
    
    init(movies: [Movie]) {
        data = movies
        super.init(style: .plain)
    }
    
    required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") }
    
    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        tableView.deselectRow(at: indexPath, animated: true)
    }
    
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return data.count
    }
    
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = makeCell(tableView)
        cell.textLabel?.text = data[indexPath.row].title
        cell.imageView?.loadImage(url: data[indexPath.row].thumbnail, placeholder: "placeholder")
        return cell
    }
    
    func makeCell(_ tableView: UITableView) -> UITableViewCell {
        guard let cell = tableView.dequeueReusableCell(withIdentifier: cellIdentifier) else {
            return MovieCell()
        }
        return cell
    }
}

class LoadingView: UIView {
    var loadingLabel: UILabel = {
        let label = UILabel()
        label.text = "Loading..."
        label.translatesAutoresizingMaskIntoConstraints = false
        return label
    }()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = UIColor.white
        addSubview(loadingLabel)
        addConstraints([
            contstraint(.centerX, from: loadingLabel, to: self),
            contstraint(.centerY, from: loadingLabel, to: self),
        ])
    }
    
    required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") }
}

class RootViewController: UIViewController {
    var movieListVC: MoviesListViewController! = nil
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view = LoadingView(frame: view.frame)
        view.backgroundColor = #colorLiteral(red: 0.8039215803, green: 0.8039215803, blue: 0.8039215803, alpha: 1)
    }

    func loadMoviesAndPresent() {
        loadMovies() { [weak self] movies in
            guard self != nil else {
                return
            }
            print("Loaded \(movies.count) movies")
            self!.movieListVC = MoviesListViewController(movies: movies)
            self!.movieListVC.modalTransitionStyle = .crossDissolve
            self!.show(self!.movieListVC, sender: self)
        }
    }
}

let rootVC = RootViewController(nibName: nil, bundle: nil)
rootVC.loadMoviesAndPresent()
PlaygroundPage.current.liveView = rootVC