Protocol-Oriented MVVM

With Swift 2.0 came Protocol Extensions, which make Swift a Protocol-Oriented Programming Language. Learn what that means and how to apply protocol extensions to create beautiful and robust code without ever defaulting to subclassing.

By Natasha the Robot http://natashatherobot.com

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1. POMVVM @NATASHATHEROBOT
4. "Swift Is a Protocol-Oriented Programming Language" — Dave Abrahams, Professor of Blowing-Your-Mind
5. UITableViewDelegate UITableViewDataSource UITextFieldDelegate NSURLSessionDelegate CLLocationManagerDelegate MCSessionDelegate
6. !
7. !
8. !
9. !
10. Artsy Engineering: MVVM in Swift
11. MODEL let amount = 6729383.99
12. VIEW Your balance is $6,729,383.99
13. VIEWMODEL struct AccountViewModel { let displayBalance: String init(model: BankAccount) { let formattedBalance = model.balance.currencyValue displayBalance = "Your balance is \(formattedBalance)" } }
14. VIEWCONTROLLER var viewModel = ViewModel(model: Account)
18. VIEWCONTROLLER var viewModel = ViewModel(model: Account)
19. PROTOCOLS !!!
21. THE PROBLEM class SwitchWithTextTableViewCell: UITableViewCell { func configure( title: String, titleFont: UIFont, titleColor: UIColor, switchOn: Bool, switchColor: UIColor = .purpleColor(), onSwitchToggleHandler: onSwitchToggleHandlerType? = nil) { // configure views here } }
22. PROTOCOLS TO THE RESCUE !
23. protocol SwitchWithTextCellProtocol { var title: String { get } var titleFont: UIFont { get } var titleColor: UIColor { get } var switchOn: Bool { get } var switchColor: UIColor { get } func onSwitchTogleOn(on: Bool) }
24. extension SwitchWithTextCellProtocol { var switchColor: UIColor { return .purpleColor() } }
25. class SwitchWithTextTableViewCell: UITableViewCell { func configure(withDelegate delegate: SwitchWithTextCellProtocol) { // configure views here } }
26. struct MinionModeViewModel: SwitchWithTextCellProtocol { var title = "Minion Mode!!!" var switchOn = true var switchColor: UIColor { return .yellowColor() } func onSwitchTogleOn(on: Bool) { if on { print("The Minions are here to stay!") } else { print("The Minions went out to play!") } } }
27. CELLFORROWATINDEXPATH // YourViewController.swift let cell = tableView.dequeueReusableCellWithIdentifier("SwitchWithTextTableViewCell", forIndexPath: indexPath) as! SwitchWithTextTableViewCell // this is where the magic happens! cell.configure(withDelegate: MinionModeViewModel()) return cell
28. !
29. ✍
30. protocol SwitchWithTextCellDataSource { var title: String { get } var switchOn: Bool { get } } protocol SwitchWithTextCellDelegate { func onSwitchTogleOn(on: Bool) var switchColor: UIColor { get } var textColor: UIColor { get } var font: UIFont { get } }
31. // SwitchWithTextTableViewCell func configure(withDataSource dataSource: SwitchWithTextCellDataSource, delegate: SwitchWithTextCellDelegate?) { // configure views here }
32. struct MinionModeViewModel: SwitchWithTextCellDataSource { var title = "Minion Mode!!!" var switchOn = true }
33. extension MinionModeViewModel: SwitchWithTextCellDelegate { var switchColor: UIColor { return .yellowColor() } func onSwitchTogleOn(on: Bool) { if on { print("The Minions are here to stay!") } else { print("The Minions went out to play!") } } }
34. // SettingsViewController let viewModel = MinionModeViewModel() cell.configure(withDataSource: viewModel, delegate: viewModel) return cell
35. !
36. @MHOLLEMANS: MIXINS AND TRAITS IN SWIFT 2.0
39. class AIPlayer: GameObject, AITrait, GunTrait, RenderTrait, HealthTrait { ... } class ZapMonster: GameObject, GunTrait, RenderTrait, HealthTrait, MovementTrait { ... }
40. ! "
41. protocol TextPresentable { var text: String { get } var textColor: UIColor { get } var font: UIFont { get } } protocol SwitchPresentable { var switchOn: Bool { get } var switchColor: UIColor { get } func onSwitchTogleOn(on: Bool) }
42. protocol ImagePresentable { var imageName: String { get } } protocol TextFieldPresentable { var placeholder: String { get } var text: String { get } func onTextFieldDidEndEditing(textField: UITextField) }
43. extension TextPresentable { var textColor: UIColor { return .blackColor() } var font: UIFont { return .systemFontOfSize(17) } }
44. !!! class SwitchWithTextTableViewCell<T where T: TextPresentable, T: SwitchPresentable>: UITableViewCell { private var delegate: T? func configure(withDelegate delegate: T) { // configure views here } }
45. extension MinionModeViewModel: TextPresentable { var text: String { return "Minion Mode" } var textColor: UIColor { return .blackColor() } var font: UIFont { return .systemFontOfSize(17.0) } }
46. extension MinionModeViewModel: SwitchPresentable { var switchOn: Bool { return false } var switchColor: UIColor { return .yellowColor() } func onSwitchTogleOn(on: Bool) { if on { print("The Minions are here to stay!") } else { print("The Minions went out to play!") } } }
47. let cell = tableView.dequeueReusableCellWithIdentifier("SwitchWithTextTableViewCell", forIndexPath: indexPath) as! SwitchWithTextTableViewCell<MinionModeViewModel> let viewModel = MinionModeViewModel() cell.configure(withDelegate: viewModel) return cell
48. !"#
49. "Change is the only constant." — Unknown
51. class SwitchWithTextTableViewCell<T where T: TextPresentable, T: SwitchPresentable, T: ImagePresentable>: UITableViewCell { }
52. extension MinionModeViewModel: ImagePresentable { var imageName: String { return "minionParty.png" } }
53. !"
54. > Use Protocols to Configure Your Views > Use Protocol Extensions for Defaults > Use ViewModels to Provide Data for the Protocols
55. HOW CAN WE MAKE THIS BETTER?