MVVM Pattern

MVVMPlayground.swift

import UIKit

struct Article {
  var title: String
  var body: String
  var date: NSDate
  var saved: Bool
  var thumbnail: NSURL
}

protocol ArticleViewViewModel {
  var title: String { get }
  var body: String { get }
  var date: String { get }
  var thumbnail: UIImage? { get }
}

struct ArticleViewViewModelFromArticle: ArticleViewViewModel {
  let article: Article
  let title: String
  let body: String
  let date: String
  var thumbnail: UIImage?
  
  init(_ article: Article) {
    self.article = article
    
    self.title = article.title
    self.body = article.body
    
    let dateFormatter = NSDateFormatter()
    dateFormatter.dateStyle = NSDateFormatterStyle.ShortStyle
    self.date = dateFormatter.stringFromDate(article.date)
    
    let downloadTask = NSURLSession.sharedSession().downloadTaskWithURL(article.thumbnail) {
      location, response, error -> Void in
      if let data = NSData(contentsOfURL: location!) {
        if let image = UIImage(data: data) {
          self.thumbnail = image
        }
      }
    }
    downloadTask.resume()
  }
}

// this would normally take the ViewController delegates
class ArticleViewController {
  var bodyTextView: UITextView!
  var titleLabel: UILabel!
  var dateLabel: UILabel!
  var thumbnailImageView: UIImageView!
  
  var viewModel: ArticleViewViewModel! {
    didSet {
      titleLabel.text = viewModel.title
      bodyTextView.text = viewModel.body
      dateLabel.text = viewModel.date
      thumbnailImageView.image = viewModel.thumbnail
    }
  }
  
  init() {
  }
}

let article = Article(title: "title text", body: "lorem ipsum", date: NSDate(), saved: true, thumbnail: NSURL(string: "www.google.com")!)
let viewModel = ArticleViewViewModelFromArticle(article)
let viewController = ArticleViewController()
viewController.viewModel = viewModel