MVVM as a good (anti)pattern in iOS - RSConf 2019

Nowadays there are a lot of materials, presentations & talks about how great MVVM architecture is. The hype about the view models looks like a never-ending story. There are a lot of developers who like this approach and use it in their own projects. I tried to go against the grain and show a different perspective of MVVM.

Transcript

1. MVVM as a good (anti)pattern in iOS @SzklarekMateusz RSConf 2019
2. Mateusz Szklarek Senior iOS Developer @elpassion (Warsaw) mateuszszklarek @SzklarekMateusz @SzklarekMateusz RSConf 2019 2
3. Agenda 1. Short explanation WHY? 2. MVVM - where it comes from? 3. MVVM in i OS World 4. Alternative solutions 5. Conclusions 6. Q & A @SzklarekMateusz RSConf 2019 3
4. WHY anti pattern? What's wrong with MVVM? @SzklarekMateusz RSConf 2019 4
5. NOTHING @SzklarekMateusz RSConf 2019 5
6. There is nothing wrong with MVVM itself... @SzklarekMateusz RSConf 2019 6
7. SOLID @SzklarekMateusz RSConf 2019 7
8. The thing which motivates me to do this talk was... @SzklarekMateusz RSConf 2019 8
9. Swift code @SzklarekMateusz RSConf 2019 9
10. Swift code @SzklarekMateusz RSConf 2019 10
11. Swift code 4 including mine 3 years ago, @SzklarekMateusz RSConf 2019 10
12. Swift code 4 including mine 3 years ago, 4 in other companies, @SzklarekMateusz RSConf 2019 10
13. Swift code 4 including mine 3 years ago, 4 in other companies, 4 open source projects available on github, @SzklarekMateusz RSConf 2019 10
14. Swift code 4 including mine 3 years ago, 4 in other companies, 4 open source projects available on github, 4 tons of articles which promote MVVM. @SzklarekMateusz RSConf 2019 10
15. Let's start from the beginning @SzklarekMateusz RSConf 2019 11
16. MVVM Model-View-ViewModel @SzklarekMateusz RSConf 2019 12
17. @SzklarekMateusz RSConf 2019 13
18. Who? When? @SzklarekMateusz RSConf 2019 14
19. Invented by Microsoft architects Ken Cooper & Ted Peters to simplify event-driven programming of user interfaces. @SzklarekMateusz RSConf 2019 15
20. Introduced for the first time in 2005 by John Gossman - one of Microsoft's WPF1 and Silverlight architects. 1 Windows Presentation Foundation @SzklarekMateusz RSConf 2019 16
21. Windows Presentation Foundation is a graphical subsystem created by Microsoft for rendering user interfaces in Windows-based applications. Released as part of .NET Framework 3.0 in 2006. @SzklarekMateusz RSConf 2019 17
22. Basic approach of MVVM in WPF @SzklarekMateusz RSConf 2019 18
23. public class CustomerViewModel { private Customer obj = new Customer(); public string TxtCustomerName { get { return obj.CustomerName; } set { obj.CustomerName = value; } } public string TxtAmount { get { return Convert.ToString(obj.Amount) ; } set { obj.Amount = Convert.ToDouble(value); } } ... } @SzklarekMateusz RSConf 2019 19
24. public class CustomerViewModel { ... public string LblAmountColor { get { if (obj.Amount > 2000) { return "Blue"; } else if (obj.Amount > 1500) { return "Red"; } return "Yellow"; } } public bool IsMarried { get { if (obj.Married == "Married") { return true; } else { return false; } } } } @SzklarekMateusz RSConf 2019 20
25. private void DisplayUi(CustomerViewModel customer) { lblName.Content = customer.TxtCustomerName; lblAmount.Content = customer.TxtAmount; BrushConverter brushconv = new BrushConverter(); lblBuyingHabits.Background = brushconv.ConvertFromString(customer.LblAmountColor) as SolidColorBrush; chkMarried.IsChecked = customer.IsMarried; } @SzklarekMateusz RSConf 2019 21
26. @SzklarekMateusz RSConf 2019 22
27. @SzklarekMateusz RSConf 2019 23
28. You don't even need to write this binding code @SzklarekMateusz RSConf 2019 24
29. @SzklarekMateusz RSConf 2019 25
30. Gossman introduced MVVM as a standardized way to leverage core features of WPF to simplify the creation of user interfaces. In that sense, I consider MVVM to be a tailor-made for the WPF and Silverlight platforms. -- Josh Smith (Microsoft), February 2009 @SzklarekMateusz RSConf 2019 26
31. MVVM in iOS @SzklarekMateusz RSConf 2019 27
32. @SzklarekMateusz RSConf 2019 28
33. ViewModel means different things for different people @SzklarekMateusz RSConf 2019 29
34. 2 different definitions @SzklarekMateusz RSConf 2019 30
35. View model is an abstract object between a model object and a view controller, which performs any data transformation necssary for presentation, as well as sometimes networking and database access, might do a little form validation and any other tasks you feel like throwing in there, and acts as a jack-of-all-trades object originally intended to transfer weight away from your controllers but ultimately creates a new kitchen sink for you to dump responsibilities into. Soroush Khanlou @SzklarekMateusz RSConf 2019 31
36. class SavedListViewModel { var title: String // MARK: Child view models var itemViewModels: [SavedListItemViewModel] {} var loadMoreViewModel: FetchMoreViewModel? {} // MARK: Loading var isLoading: Bool {} var isPerformingAction: Bool {} // MARK: Actions func present(details: PropertyDTO) {...} func itemLeftButtonAction(itemViewModel: SavedListItemViewModel) {...} func itemRightButtonAction(itemViewModel: SavedListItemViewModel) {...} // MARK: Networking func reloadItems() {} func loadMoreItems() {} } @SzklarekMateusz RSConf 2019 32
37. class SavedListViewModel { var title: String // MARK: Child view models var itemViewModels: [SavedListItemViewModel] {} var loadMoreViewModel: FetchMoreViewModel? {} // MARK: Loading var isLoading: Bool {} var isPerformingAction: Bool {} // MARK: Actions func present(details: PropertyDTO) {...} func itemLeftButtonAction(itemViewModel: SavedListItemViewModel) {...} func itemRightButtonAction(itemViewModel: SavedListItemViewModel) {...} // MARK: Networking func reloadItems() {} func loadMoreItems() {} } @SzklarekMateusz RSConf 2019 32
38. class EventsViewModel { var lastEvent: Observable<Event?> var buttonsState: Observable<ButtonsState> var tableViewState: Observable<AppContentState> var isReminderAllowed: Bool var isEventOutdated: Bool var attendanceState: Observable<AttendanceState> var notificationState: Observable<NotificationState> var facebookAlert: Observable<String?> var loginScreen: Observable<Void> var summaryCellDidTap: Observable<Void> var locationCellDidTap: Observable<Void> var eventsListRefresh: Observable<Void> var previousEventsCellDidSet: Observable<Void> var previousEventsViewModel: Observable<PreviousEventsListTableViewCellViewModel?> var previousEvents: Observable<[Event?]?> var eventDetailsRefresh: Observable<Void>() var carouselEventPhotosViewModel: Observable<CarouselEventPhotosTableViewCellViewModel?> var lectureCellDidTap: Observable<Int> var speakerCellDidTap: Observable<Int> var notificationPermissionsNotGranted: Observable<Void>() weak var delegate: EventsControllerDelegate? } @SzklarekMateusz RSConf 2019 33
39. What is wrong with it? @SzklarekMateusz RSConf 2019 34
40. class EventsViewModel { var buttonsState: Observable<ButtonsState> var tableViewState: Observable<AppContentState> var attendanceState: Observable<AttendanceState> var isReminderAllowed: Bool var isEventOutdated: Bool var facebookAlert: Observable<String?> var loginScreen: Observable<Void> var summaryCellDidTap: Observable<Void> var locationCellDidTap: Observable<Void> var lectureCellDidTap: Observable<Int> var speakerCellDidTap: Observable<Int> var eventsListRefresh: Observable<Void> var eventDetailsRefresh: Observable<Void> var previousEventsCellDidSet: Observable<Void> var previousEvents: Observable<[Event?]?> var previousEventsViewModel: Observable<PreviousEventsListTableViewCellViewModel?> var carouselEventPhotosViewModel: Observable<CarouselEventPhotosTableViewCellViewModel?> var lastEvent: Observable<Event?> weak var delegate: EventsControllerDelegate? var notificationState: Observable<NotificationState> var notificationPermissionsNotGranted: Observable<Void> } @SzklarekMateusz RSConf 2019 35
41. class EventsViewModel { var buttonsState: Observable<ButtonsState> var tableViewState: Observable<AppContentState> var attendanceState: Observable<AttendanceState> var isReminderAllowed: Bool var isEventOutdated: Bool var facebookAlert: Observable<String?> var loginScreen: Observable<Void> var summaryCellDidTap: Observable<Void> var locationCellDidTap: Observable<Void> var lectureCellDidTap: Observable<Int> var speakerCellDidTap: Observable<Int> var eventsListRefresh: Observable<Void> var eventDetailsRefresh: Observable<Void> var previousEventsCellDidSet: Observable<Void> var previousEvents: Observable<[Event?]?> var previousEventsViewModel: Observable<PreviousEventsListTableViewCellViewModel?> var carouselEventPhotosViewModel: Observable<CarouselEventPhotosTableViewCellViewModel?> var lastEvent: Observable<Event?> weak var delegate: EventsControllerDelegate? var notificationState: Observable<NotificationState> var notificationPermissionsNotGranted: Observable<Void> } @SzklarekMateusz RSConf 2019 35
42. class EventsViewModel { var buttonsState: Observable<ButtonsState> var tableViewState: Observable<AppContentState> var attendanceState: Observable<AttendanceState> var isReminderAllowed: Bool var isEventOutdated: Bool var facebookAlert: Observable<String?> var loginScreen: Observable<Void> var summaryCellDidTap: Observable<Void> var locationCellDidTap: Observable<Void> var lectureCellDidTap: Observable<Int> var speakerCellDidTap: Observable<Int> var eventsListRefresh: Observable<Void> var eventDetailsRefresh: Observable<Void> var previousEventsCellDidSet: Observable<Void> var previousEvents: Observable<[Event?]?> var previousEventsViewModel: Observable<PreviousEventsListTableViewCellViewModel?> var carouselEventPhotosViewModel: Observable<CarouselEventPhotosTableViewCellViewModel?> var lastEvent: Observable<Event?> weak var delegate: EventsControllerDelegate? var notificationState: Observable<NotificationState> var notificationPermissionsNotGranted: Observable<Void> } @SzklarekMateusz RSConf 2019 35
43. class EventsViewModel { var buttonsState: Observable<ButtonsState> var tableViewState: Observable<AppContentState> var attendanceState: Observable<AttendanceState> var isReminderAllowed: Bool var isEventOutdated: Bool var facebookAlert: Observable<String?> var loginScreen: Observable<Void> var summaryCellDidTap: Observable<Void> var locationCellDidTap: Observable<Void> var lectureCellDidTap: Observable<Int> var speakerCellDidTap: Observable<Int> var eventsListRefresh: Observable<Void> var eventDetailsRefresh: Observable<Void> var previousEventsCellDidSet: Observable<Void> var previousEvents: Observable<[Event?]?> var previousEventsViewModel: Observable<PreviousEventsListTableViewCellViewModel?> var carouselEventPhotosViewModel: Observable<CarouselEventPhotosTableViewCellViewModel?> var lastEvent: Observable<Event?> weak var delegate: EventsControllerDelegate? var notificationState: Observable<NotificationState> var notificationPermissionsNotGranted: Observable<Void> } @SzklarekMateusz RSConf 2019 35
44. class EventsViewModel { var buttonsState: Observable<ButtonsState> var tableViewState: Observable<AppContentState> var attendanceState: Observable<AttendanceState> var isReminderAllowed: Bool var isEventOutdated: Bool var facebookAlert: Observable<String?> var loginScreen: Observable<Void> var summaryCellDidTap: Observable<Void> var locationCellDidTap: Observable<Void> var lectureCellDidTap: Observable<Int> var speakerCellDidTap: Observable<Int> var eventsListRefresh: Observable<Void> var eventDetailsRefresh: Observable<Void> var previousEventsCellDidSet: Observable<Void> var previousEvents: Observable<[Event?]?> var previousEventsViewModel: Observable<PreviousEventsListTableViewCellViewModel?> var carouselEventPhotosViewModel: Observable<CarouselEventPhotosTableViewCellViewModel?> var lastEvent: Observable<Event?> weak var delegate: EventsControllerDelegate? var notificationState: Observable<NotificationState> var notificationPermissionsNotGranted: Observable<Void> } @SzklarekMateusz RSConf 2019 35
45. class EventsViewModel { var buttonsState: Observable<ButtonsState> var tableViewState: Observable<AppContentState> var attendanceState: Observable<AttendanceState> var isReminderAllowed: Bool var isEventOutdated: Bool var facebookAlert: Observable<String?> var loginScreen: Observable<Void> var summaryCellDidTap: Observable<Void> var locationCellDidTap: Observable<Void> var lectureCellDidTap: Observable<Int> var speakerCellDidTap: Observable<Int> var eventsListRefresh: Observable<Void> var eventDetailsRefresh: Observable<Void> var previousEventsCellDidSet: Observable<Void> var previousEvents: Observable<[Event?]?> var previousEventsViewModel: Observable<PreviousEventsListTableViewCellViewModel?> var carouselEventPhotosViewModel: Observable<CarouselEventPhotosTableViewCellViewModel?> var lastEvent: Observable<Event?> weak var delegate: EventsControllerDelegate? var notificationState: Observable<NotificationState> var notificationPermissionsNotGranted: Observable<Void> } @SzklarekMateusz RSConf 2019 35
46. class EventsViewModel { var buttonsState: Observable<ButtonsState> var tableViewState: Observable<AppContentState> var attendanceState: Observable<AttendanceState> var isReminderAllowed: Bool var isEventOutdated: Bool var facebookAlert: Observable<String?> var loginScreen: Observable<Void> var summaryCellDidTap: Observable<Void> var locationCellDidTap: Observable<Void> var lectureCellDidTap: Observable<Int> var speakerCellDidTap: Observable<Int> var eventsListRefresh: Observable<Void> var eventDetailsRefresh: Observable<Void> var previousEventsCellDidSet: Observable<Void> var previousEvents: Observable<[Event?]?> var previousEventsViewModel: Observable<PreviousEventsListTableViewCellViewModel?> var carouselEventPhotosViewModel: Observable<CarouselEventPhotosTableViewCellViewModel?> var lastEvent: Observable<Event?> weak var delegate: EventsControllerDelegate? var notificationState: Observable<NotificationState> var notificationPermissionsNotGranted: Observable<Void> } @SzklarekMateusz RSConf 2019 35
47. class EventsViewModel { var buttonsState: Observable<ButtonsState> var tableViewState: Observable<AppContentState> var attendanceState: Observable<AttendanceState> var isReminderAllowed: Bool var isEventOutdated: Bool var facebookAlert: Observable<String?> var loginScreen: Observable<Void> var summaryCellDidTap: Observable<Void> var locationCellDidTap: Observable<Void> var lectureCellDidTap: Observable<Int> var speakerCellDidTap: Observable<Int> var eventsListRefresh: Observable<Void> var eventDetailsRefresh: Observable<Void> var previousEventsCellDidSet: Observable<Void> var previousEvents: Observable<[Event?]?> var previousEventsViewModel: Observable<PreviousEventsListTableViewCellViewModel?> var carouselEventPhotosViewModel: Observable<CarouselEventPhotosTableViewCellViewModel?> var lastEvent: Observable<Event?> weak var delegate: EventsControllerDelegate? var notificationState: Observable<NotificationState> var notificationPermissionsNotGranted: Observable<Void> } @SzklarekMateusz RSConf 2019 35
48. @SzklarekMateusz RSConf 2019 36
49. @SzklarekMateusz RSConf 2019 37
50. @SzklarekMateusz RSConf 2019 38
51. class SavedListViewModel { var title: String // MARK: Child view models var itemViewModels: [SavedListItemViewModel] {} var loadMoreViewModel: FetchMoreViewModel? {} // MARK: Loading var isLoading: Bool {} var isPerformingAction: Bool {} // MARK: Actions func present(details: PropertyDTO) {...} func itemLeftButtonAction(itemViewModel: SavedListItemViewModel) {...} func itemRightButtonAction(itemViewModel: SavedListItemViewModel) {...} // MARK: Networking func reloadItems() {} func loadMoreItems() {} } @SzklarekMateusz RSConf 2019 39
52. Implementation (numbers) @SzklarekMateusz RSConf 2019 40
53. Implementation (numbers) 4 ViewController - 115 lines @SzklarekMateusz RSConf 2019 40
54. Implementation (numbers) 4 ViewController - 115 lines 4 bindings 190 lines @SzklarekMateusz RSConf 2019 40
55. Implementation (numbers) 4 ViewController - 115 lines 4 bindings 190 lines 4 ViewModel 280 lines @SzklarekMateusz RSConf 2019 40
56. "It's NOT a mistake to make a mistake but it is a mistake to repeat a mistake." @SzklarekMateusz RSConf 2019 41
57. @SzklarekMateusz RSConf 2019 42
58. View model is a model for a view, isn't it? @SzklarekMateusz RSConf 2019 43
59. @SzklarekMateusz RSConf 2019 44
60. View model is a “model for the view”. This is a dumb object (usually a struct in Swift) that is passed to a view to populate its subviews. Soroush Khanlou @SzklarekMateusz RSConf 2019 45
61. struct SavedListViewModel { let title: String let itemViewModels: [SavedListItemViewModel] let loadMoreViewModel: FetchMoreViewModel? let isLoading: Bool {} let isPerformingAction: Bool {} } @SzklarekMateusz RSConf 2019 46
62. struct ActivityViewModel { let id: Int let time: String let title: NSAttributedString let icon: UIImage let details: [ActivityDetailViewModel] let isSeparatorVisible: Bool } @SzklarekMateusz RSConf 2019 47
63. struct SavedListViewModel { let title: String let itemViewModels: [SavedListItemViewModel] let loadMoreViewModel: FetchMoreViewModel? let isLoading: Bool {} let isPerformingAction: Bool {} } @SzklarekMateusz RSConf 2019 48
64. What about those action methods? @SzklarekMateusz RSConf 2019 49
65. // MARK: Actions func present(details: PropertyDTO) {...} func itemLeftButtonAction(itemViewModel: SavedListItemViewModel) {...} func itemRightButtonAction(itemViewModel: SavedListItemViewModel) {...} func reloadItems() {} func loadMoreItems() {} @SzklarekMateusz RSConf 2019 50
66. UViewCon er @SzklarekMateusz RSConf 2019 51
67. MVC - Model View Controller @SzklarekMateusz RSConf 2019 52
68. MVC - Massive View Controller @SzklarekMateusz RSConf 2019 53
69. @SzklarekMateusz RSConf 2019 54
70. @SzklarekMateusz RSConf 2019 55
71. MVC - Many View Controllers @SzklarekMateusz RSConf 2019 56
72. Real life example app @SzklarekMateusz RSConf 2019 57
73. Real life example app 4 235k lines of code (85k production code & 150k tests) @SzklarekMateusz RSConf 2019 57
74. Real life example app 4 235k lines of code (85k production code & 150k tests) 4 6092 swift files @SzklarekMateusz RSConf 2019 57
75. Real life example app 4 235k lines of code (85k production code & 150k tests) 4 6092 swift files 4 8200 unit tests @SzklarekMateusz RSConf 2019 57
76. Real life example app 4 235k lines of code (85k production code & 150k tests) 4 6092 swift files 4 8200 unit tests 4 204 UIViewControllers @SzklarekMateusz RSConf 2019 57
77. Real life example app 4 235k lines of code (85k production code & 150k tests) 4 6092 swift files 4 8200 unit tests 4 204 UIViewControllers 4 average file length 37.23 lines @SzklarekMateusz RSConf 2019 57
78. Real life example app 4 235k lines of code (85k production code & 150k tests) 4 6092 swift files 4 8200 unit tests 4 204 UIViewControllers 4 average file length 37.23 lines 4 code coverage 99.2% @SzklarekMateusz RSConf 2019 57
79. Real life example app 4 235k lines of code (85k production code & 150k tests) 4 6092 swift files 4 8200 unit tests 4 204 UIViewControllers 4 average file length 37.23 lines 4 code coverage 99.2% 4 file > 150 lines does not compile (only 88 files > 100 lines) @SzklarekMateusz RSConf 2019 57
80. ? @SzklarekMateusz RSConf 2019 58
81. ViewController @SzklarekMateusz RSConf 2019 59
82. Split a view model @SzklarekMateusz RSConf 2019 60
83. Split a view model 4 Services for network calls @SzklarekMateusz RSConf 2019 60
84. Split a view model 4 Services for network calls 4 Data providers @SzklarekMateusz RSConf 2019 60
85. Split a view model 4 Services for network calls 4 Data providers 4 Notification handlers @SzklarekMateusz RSConf 2019 60
86. Split a view model 4 Services for network calls 4 Data providers 4 Notification handlers 4 Database repositories @SzklarekMateusz RSConf 2019 60
87. Split a view model 4 Services for network calls 4 Data providers 4 Notification handlers 4 Database repositories 4 and many child controllers @SzklarekMateusz RSConf 2019 60
88. Real life bugs @SzklarekMateusz RSConf 2019 61
89. @SzklarekMateusz RSConf 2019 62
90. override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) { let item = items[indexPath.row] let controller = DetailViewController(item: item) navigationController?.pushViewController(controller, animated: true) } @SzklarekMateusz RSConf 2019 63
91. public class ItemViewModel { let id: Int let title: String var buttonTapped: (() -> Void)? func presentAlert(on controller: UIViewController) { let alert = UIAlertController(title: "Confirmation", message: "Do you want to buy \(title)?", preferredStyle: .alert) alert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil)) alert.addAction(UIAlertAction(title: "YES", style: .default, handler: { [weak self] in self?.buyProduct(id: id) })) controller.present(alert, animated: true, completion: nil) } func buyProduct(id: Int) { // TODO: Network request } } @SzklarekMateusz RSConf 2019 64
92. @SzklarekMateusz RSConf 2019 65
93. @SzklarekMateusz RSConf 2019 66
94. VC => VM and VC <= VM @SzklarekMateusz RSConf 2019 67
95. @SzklarekMateusz RSConf 2019 68
96. How many view controllers are there? @SzklarekMateusz RSConf 2019 69
97. @SzklarekMateusz RSConf 2019 70
98. public class DashboardController: UIViewController { public init(childrenFactory: DashboardChildrenFactoryProtocol) { self.childrenFactory = childrenFactory super.init(nibName: nil, bundle: nil) } ... // MARK: - Child controllers private lazy var headerController = childrenFactory.makeHeaderController() private lazy var detailsController = childrenFactory.makedetailsController() private lazy var availableItemsController = childrenFactory.makeAvailableItemsController() private lazy var orderController = childrenFactory.makeOrderController() private lazy var showMoreButtonController = childrenFactory.makeReferralButtonController() ... } @SzklarekMateusz RSConf 2019 71
99. public class DashboardController: UIViewController { ... private var childControllers: [DashboardChildControllerType] { return [headerController, detailsController, availableItemsController, orderController, showMoreButtonController] } // MARK: - Lifecycle public override func viewDidLoad() { super.viewDidLoad() embedChildControllers() } // MARK: - Private private let childrenFactory: DashboardChildrenFactoryProtocol private func embedChildControllers() { childControllers.forEach { controller in embed(childViewController: controller, using: dashboardView.stackView.addArrangedSubview) } } } @SzklarekMateusz RSConf 2019 72
100. Favourites statements @SzklarekMateusz RSConf 2019 73
101. 1. "Get rid of Massive ViewController" @SzklarekMateusz RSConf 2019 74
102. small View Controller + ... @SzklarekMateusz RSConf 2019 75
103. small View Controller + massive View Model @SzklarekMateusz RSConf 2019 76
104. "Extracting logic from VC to VM is nothing else than moving the Junk to a Different Drawer" @SzklarekMateusz RSConf 2019 77
105. class ListController: UIViewController, UITableViewDataSource { ... // MARK: UITableViewDataSource override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell { let model = viewModel[indexPath.row] let cell = tableView.dequeueReusableCell(SomeCell.self, forIndexPath: indexPath) cell.model = model return cell } override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) { let model = viewModel[indexPath.row] openDetails(model: model) } ... } @SzklarekMateusz RSConf 2019 78
106. extension ListController: UITableViewDataSource { override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell { let model = viewModel[indexPath.row] let cell = tableView.dequeueReusableCell(SomeCell.self, forIndexPath: indexPath) cell.model = model return cell } override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) { let model = viewModel[indexPath.row] openDetails(model: model) } } @SzklarekMateusz RSConf 2019 79
107. 2. "MVVM makes my apps more testable" @SzklarekMateusz RSConf 2019 80
108. @SzklarekMateusz RSConf 2019 81
109. 4 John: "We do MVVM because it's really easy to test our view models" @SzklarekMateusz RSConf 2019 81
110. 4 John: "We do MVVM because it's really easy to test our view models" 4 Me: Ok, so please show me the tests @SzklarekMateusz RSConf 2019 81
111. 4 John: "We do MVVM because it's really easy to test our view models" 4 Me: Ok, so please show me the tests 4 John: We don't have them :D @SzklarekMateusz RSConf 2019 81
112. 4 John: "We do MVVM because it's really easy to test our view models" 4 Me: Ok, so please show me the tests 4 John: We don't have them :D 4 Me: Why? @SzklarekMateusz RSConf 2019 81
113. 4 John: "We do MVVM because it's really easy to test our view models" 4 Me: Ok, so please show me the tests 4 John: We don't have them :D 4 Me: Why? 4 John: Because logic is quite simple @SzklarekMateusz RSConf 2019 81
114. 4 John: "We do MVVM because it's really easy to test our view models" 4 Me: Ok, so please show me the tests 4 John: We don't have them :D 4 Me: Why? 4 John: Because logic is quite simple 4 Me: But you said that you made view models to extract business logic from your view controllers because it was too complex, am I right? @SzklarekMateusz RSConf 2019 81
115. 4 John: "We do MVVM because it's really easy to test our view models" 4 Me: Ok, so please show me the tests 4 John: We don't have them :D 4 Me: Why? 4 John: Because logic is quite simple 4 Me: But you said that you made view models to extract business logic from your view controllers because it was too complex, am I right? 4 John: Yes, it's true and it is easy to test @SzklarekMateusz RSConf 2019 81
116. with MVVM more testable without MVVM less testable? @SzklarekMateusz RSConf 2019 82
117. REALLY? @SzklarekMateusz RSConf 2019 83
118. 3. "Because it's so popular and it's a perfect solution with RxSwift" @SzklarekMateusz RSConf 2019 84
119. @SzklarekMateusz RSConf 2019 85
120. Advantages @SzklarekMateusz RSConf 2019 86
121. 4 nice way to keep the state of the view (simple struct) @SzklarekMateusz RSConf 2019 87
122. struct BookViewModel { let id: String let name: String let author: String let coverImage: UIImage } @SzklarekMateusz RSConf 2019 88
123. Disadvantages @SzklarekMateusz RSConf 2019 89
124. Break SRP @SzklarekMateusz RSConf 2019 90
125. Break SRP 4 Loading data from multiple APIs / endpoints @SzklarekMateusz RSConf 2019 90
126. Break SRP 4 Loading data from multiple APIs / endpoints 4 Filtering data @SzklarekMateusz RSConf 2019 90
127. Break SRP 4 Loading data from multiple APIs / endpoints 4 Filtering data 4 logic for formatting strings (composed from several other values) @SzklarekMateusz RSConf 2019 90
128. Break SRP 4 Loading data from multiple APIs / endpoints 4 Filtering data 4 logic for formatting strings (composed from several other values) 4 Being data sources and delegates for UITableViews / UICollectionViews @SzklarekMateusz RSConf 2019 90
129. Break SRP 4 Loading data from multiple APIs / endpoints 4 Filtering data 4 logic for formatting strings (composed from several other values) 4 Being data sources and delegates for UITableViews / UICollectionViews 4 Saving or persisting data @SzklarekMateusz RSConf 2019 90
130. 4 Break SRP 4 Poor reusability @SzklarekMateusz RSConf 2019 91
131. 4 Break SRP 4 Poor reusability 4 Poor testability @SzklarekMateusz RSConf 2019 92
132. 4 Break SRP 4 Poor reusability 4 Poor testability 4 without bindings it's still more code to write @SzklarekMateusz RSConf 2019 93
133. 3 things to remember @SzklarekMateusz RSConf 2019 94
134. 3 things to remember 4 architecture & design patterns are to solve problem not to create them @SzklarekMateusz RSConf 2019 94
135. 3 things to remember 4 architecture & design patterns are to solve problem not to create them 4 don't put network calls, logic and different actions to your view model - use your view model as a simple struct @SzklarekMateusz RSConf 2019 94
136. 3 things to remember 4 architecture & design patterns are to solve problem not to create them 4 don't put network calls, logic and different actions to your view model - use your view model as a simple struct 4 don't repeat mistakes from your previous projects @SzklarekMateusz RSConf 2019 94
137. References https://blogs.msdn.microsoft.com/johngossman/2005/10/08/introduction- to-modelviewviewmodel-pattern-for-building-wpf-apps/ https://msdn.microsoft.com/en-us/magazine/dd419663.aspx https://wpf.2000things.com/tag/code-behind/ https://www.objc.io/issues/13-architecture/mvvm/ https://medium.com/flawless-app-stories/how-to-use-a-model-view- viewmodel-architecture-for-ios-46963c67be1b http://www.danielhall.io/the-problems-with-mvvm-on-ios http://khanlou.com/2015/12/mvvm-is-not-very-good/ @SzklarekMateusz RSConf 2019 95
138. Mateusz Szklarek Senior iOS Developer @elpassion (Warsaw) mateuszszklarek @SzklarekMateusz @SzklarekMateusz RSConf 2019 96