coalescing-updates-playground-done.swift

import UIKit
import PlaygroundSupport

extension NSNotification.Name {
    static let todoListItemUpdated = NSNotification.Name("TodoListItemUpdated")
}

class TodoList {
    static let shared = TodoList()

    var items: [TodoListItem] = [
        TodoListItem(title: "Wash dishes"),
        TodoListItem(title: "Take out garbage"),
        TodoListItem(title: "Go grocery shopping"),
        TodoListItem(title: "Do laundry"),
        TodoListItem(title: "Meal prep for next week")
    ]

    func markAllAsCompleted() {
        for item in items {
            item.completed = true
        }
    }
}

class TodoListItem {
    let title: String

    var completed: Bool = false {
        didSet {
            NotificationCenter.default.post(name: .todoListItemUpdated, object: self)
        }
    }

    init(title: String) {
        self.title = title
    }
}

class ViewController: UITableViewController {
    let dispatchSource = DispatchSource.makeUserDataAddSource(queue: .main)

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationItem.title = "To Do..."
        navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Complete All", style: .plain, target: self, action: #selector(completeAll))

        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "Cell")

        dispatchSource.setEventHandler(handler: { [weak self] in
            print("tableView.reloadData()")
            self?.tableView.reloadData()
        })
        dispatchSource.resume()

        NotificationCenter.default.addObserver(self, selector: #selector(todoListItemUpdated), name: .todoListItemUpdated, object: nil)
    }

    @objc func completeAll() {
        TodoList.shared.markAllAsCompleted()
    }

    @objc func todoListItemUpdated() {
        dispatchSource.add(data: 1)
    }

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

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
        let item = TodoList.shared.items[indexPath.row]
        if item.completed {
            cell.textLabel?.text = "✅  " + item.title
        }
        else {
            cell.textLabel?.text = item.title
        }
        return cell
    }

    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        tableView.deselectRow(at: indexPath, animated: false)
        TodoList.shared.items[indexPath.row].completed.toggle()
    }
}

PlaygroundPage.current.liveView = UINavigationController(rootViewController: ViewController())
PlaygroundPage.current.needsIndefiniteExecution = true