mantledata-illustration.swift

// View model for each tweets.
class TweetViewModel {
	let username: AnyProperty<String>
	let content: AnyProperty<String>
	let date: AnyProperty<String>

	init(tweet: tweet, controller: controller) {
		let dateFormatter = { … }
		username = AnyProperty(tweet.property(forKeyPath: #keyPath(Tweet.name)))
		content = AnyProperty(tweet.property(forKeyPath: #keyPath(Tweet.content)))
		date = tweet.property(forKeyPath: #keyPath(Tweet.date), type: Date.self)
			.map(dateFormatter)
	}
}

// View model for a timeline of tweets.
class TimelineViewModel {
	let tweets: ViewModelSet<TweetViewModel>

	init(controller: TimelineController) {
		let tweetObjects = Tweet.query(controller.mainContext)
			.group(by: .descending(keyPath: "date"))
			.sort(by: .descending(keyPath: "datetime"))
			.makeObjectSet()

		tweets = ViewModelSet(tweetsObjects) { tweet in
			return TweetViewModel(tweet: tweet, controller: controller)
		}
	}
}

// The view controller for the timeline.
class TimelineViewController: UITableViewController {
	// setter injection.
	var viewModel: TimelineViewModel!

	func viewDidLoad {
		TableViewAdapter(set: viewModel.tweets)
			.register(for: …) { … cell.viewModel.value = $0 … }
			.bind(tableView)
	}
}