MVVM as a good (anti)pattern in iOS - Mobilization IX 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 Mobilization IX 2019
2. Mateusz Szklarek Senior iOS Developer @elpassion (Warsaw) mateuszszklarek @SzklarekMateusz @SzklarekMateusz Mobilization IX 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 Mobilization IX 2019 3
4. Questionaire @SzklarekMateusz Mobilization IX 2019 4
5. How many of you use MVVM and like it? @SzklarekMateusz Mobilization IX 2019 5
6. How many of you have unit tests for view models? @SzklarekMateusz Mobilization IX 2019 6
7. How many of you write unit tests? @SzklarekMateusz Mobilization IX 2019 7
8. How many of you write tests before real implementation (TDD)? @SzklarekMateusz Mobilization IX 2019 8
9. WHY anti pattern? What's wrong with MVVM? @SzklarekMateusz Mobilization IX 2019 9
10. NOTHING @SzklarekMateusz Mobilization IX 2019 10
11. There is nothing wrong with MVVM itself... @SzklarekMateusz Mobilization IX 2019 11
12. SOLID @SzklarekMateusz Mobilization IX 2019 12
13. The thing which motivates me to do this talk was... @SzklarekMateusz Mobilization IX 2019 13
14. Swift code @SzklarekMateusz Mobilization IX 2019 14
15. Swift code @SzklarekMateusz Mobilization IX 2019 15
16. Swift code 4 including mine 3 years ago, @SzklarekMateusz Mobilization IX 2019 15
17. Swift code 4 including mine 3 years ago, 4 in other companies, @SzklarekMateusz Mobilization IX 2019 15
18. Swift code 4 including mine 3 years ago, 4 in other companies, 4 open source projects available on github, @SzklarekMateusz Mobilization IX 2019 15
19. 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 Mobilization IX 2019 15
20. Let's start from the beginning @SzklarekMateusz Mobilization IX 2019 16
21. MVVM Model-View-ViewModel @SzklarekMateusz Mobilization IX 2019 17
22. @SzklarekMateusz Mobilization IX 2019 18
23. Who? When? @SzklarekMateusz Mobilization IX 2019 19
24. Invented by Microsoft architects Ken Cooper & Ted Peters to simplify event-driven programming of user interfaces. @SzklarekMateusz Mobilization IX 2019 20
25. Introduced for the first time in 2005 by John Gossman - one of Microsoft's WPF1 and Silverlight architects. 1 Windows Presentation Foundation @SzklarekMateusz Mobilization IX 2019 21
26. 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 Mobilization IX 2019 22
27. Basic approach of MVVM in WPF @SzklarekMateusz Mobilization IX 2019 23
28. 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 Mobilization IX 2019 24
29. 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 Mobilization IX 2019 25
30. 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 Mobilization IX 2019 26
31. @SzklarekMateusz Mobilization IX 2019 27
32. @SzklarekMateusz Mobilization IX 2019 28
33. You don't even need to write this binding code @SzklarekMateusz Mobilization IX 2019 29
34. @SzklarekMateusz Mobilization IX 2019 30
35. 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 Mobilization IX 2019 31
36. MVVM in iOS @SzklarekMateusz Mobilization IX 2019 32
37. @SzklarekMateusz Mobilization IX 2019 33
38. ViewModel means different things for different people @SzklarekMateusz Mobilization IX 2019 34
39. 2 different definitions @SzklarekMateusz Mobilization IX 2019 35
40. 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 Mobilization IX 2019 36
41. 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 Mobilization IX 2019 37
42. 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 Mobilization IX 2019 37
43. 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 Mobilization IX 2019 38
44. What is wrong with it? @SzklarekMateusz Mobilization IX 2019 39
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 Mobilization IX 2019 40
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 Mobilization IX 2019 40
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 Mobilization IX 2019 40
48. 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 Mobilization IX 2019 40
49. 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 Mobilization IX 2019 40
50. 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 Mobilization IX 2019 40
51. 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 Mobilization IX 2019 40
52. 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 Mobilization IX 2019 40
53. @SzklarekMateusz Mobilization IX 2019 41
54. @SzklarekMateusz Mobilization IX 2019 42
55. @SzklarekMateusz Mobilization IX 2019 43
56. 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 Mobilization IX 2019 44
57. Implementation (numbers) @SzklarekMateusz Mobilization IX 2019 45
58. Implementation (numbers) 4 ViewController - 115 lines @SzklarekMateusz Mobilization IX 2019 45
59. Implementation (numbers) 4 ViewController - 115 lines 4 bindings 190 lines @SzklarekMateusz Mobilization IX 2019 45
60. Implementation (numbers) 4 ViewController - 115 lines 4 bindings 190 lines 4 ViewModel 280 lines @SzklarekMateusz Mobilization IX 2019 45
61. "It's NOT a mistake to make a mistake but it is a mistake to repeat a mistake." @SzklarekMateusz Mobilization IX 2019 46
62. @SzklarekMateusz Mobilization IX 2019 47
63. View model is a model for a view, isn't it? @SzklarekMateusz Mobilization IX 2019 48
64. @SzklarekMateusz Mobilization IX 2019 49
65. 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 Mobilization IX 2019 50
66. struct SavedListViewModel { let title: String let itemViewModels: [SavedListItemViewModel] let loadMoreViewModel: FetchMoreViewModel? let isLoading: Bool {} let isPerformingAction: Bool {} } @SzklarekMateusz Mobilization IX 2019 51
67. struct ActivityViewModel { let id: Int let time: String let title: NSAttributedString let icon: UIImage let details: [ActivityDetailViewModel] let isSeparatorVisible: Bool } @SzklarekMateusz Mobilization IX 2019 52
68. struct SavedListViewModel { let title: String let itemViewModels: [SavedListItemViewModel] let loadMoreViewModel: FetchMoreViewModel? let isLoading: Bool {} let isPerformingAction: Bool {} } @SzklarekMateusz Mobilization IX 2019 53
69. What about those action methods? @SzklarekMateusz Mobilization IX 2019 54
70. // MARK: Actions func present(details: PropertyDTO) {...} func itemLeftButtonAction(itemViewModel: SavedListItemViewModel) {...} func itemRightButtonAction(itemViewModel: SavedListItemViewModel) {...} func reloadItems() {} func loadMoreItems() {} @SzklarekMateusz Mobilization IX 2019 55
71. UViewCon er @SzklarekMateusz Mobilization IX 2019 56
72. MVC - Model View Controller @SzklarekMateusz Mobilization IX 2019 57
73. MVC - Massive View Controller @SzklarekMateusz Mobilization IX 2019 58
74. @SzklarekMateusz Mobilization IX 2019 59
75. @SzklarekMateusz Mobilization IX 2019 60
76. MVC - Many View Controllers @SzklarekMateusz Mobilization IX 2019 61
77. Real life example app @SzklarekMateusz Mobilization IX 2019 62
78. Real life example app 4 235k lines of code (85k production code & 150k tests) @SzklarekMateusz Mobilization IX 2019 62
79. Real life example app 4 235k lines of code (85k production code & 150k tests) 4 6092 swift files @SzklarekMateusz Mobilization IX 2019 62
80. Real life example app 4 235k lines of code (85k production code & 150k tests) 4 6092 swift files 4 8200 unit tests @SzklarekMateusz Mobilization IX 2019 62
81. 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 Mobilization IX 2019 62
82. 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 Mobilization IX 2019 62
83. 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 Mobilization IX 2019 62
84. 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 Mobilization IX 2019 62
85. 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) 4 8 frameworks @SzklarekMateusz Mobilization IX 2019 62
86. ? @SzklarekMateusz Mobilization IX 2019 63
87. ViewController @SzklarekMateusz Mobilization IX 2019 64
88. Split a view model @SzklarekMateusz Mobilization IX 2019 65
89. Split a view model 4 Services for network calls @SzklarekMateusz Mobilization IX 2019 65
90. Split a view model 4 Services for network calls 4 Data providers @SzklarekMateusz Mobilization IX 2019 65
91. Split a view model 4 Services for network calls 4 Data providers 4 Notification handlers @SzklarekMateusz Mobilization IX 2019 65
92. Split a view model 4 Services for network calls 4 Data providers 4 Notification handlers 4 Database repositories @SzklarekMateusz Mobilization IX 2019 65
93. Split a view model 4 Services for network calls 4 Data providers 4 Notification handlers 4 Database repositories 4 and many child controllers @SzklarekMateusz Mobilization IX 2019 65
94. Real life bugs @SzklarekMateusz Mobilization IX 2019 66
95. @SzklarekMateusz Mobilization IX 2019 67
96. override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) { let item = items[indexPath.row] let controller = DetailViewController(item: item) navigationController?.pushViewController(controller, animated: true) } @SzklarekMateusz Mobilization IX 2019 68
97. 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 Mobilization IX 2019 69
98. @SzklarekMateusz Mobilization IX 2019 70
99. @SzklarekMateusz Mobilization IX 2019 71
100. VC => VM and VM => VC @SzklarekMateusz Mobilization IX 2019 72
101. @SzklarekMateusz Mobilization IX 2019 73
102. How many view controllers are there? @SzklarekMateusz Mobilization IX 2019 74
103. @SzklarekMateusz Mobilization IX 2019 75
104. 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 Mobilization IX 2019 76
105. 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 Mobilization IX 2019 77
106. Many View Controllers? Why not put it inside a view? @SzklarekMateusz Mobilization IX 2019 78
107. Lack of lifecycle @SzklarekMateusz Mobilization IX 2019 79
108. class DetailsView: UIView { let container: UIStackView = Subviews.container let verticalContainer: UIStackView = Subviews.verticalContainer let titleView: TitleView = TitleView() let separator: UIView = Subviews.separator let infoView: InfoView = InfoView() let icon: UIImageView = Views.imageView(contentMode: .scaleAspectFit) init() { super.init(frame: .zero) addSubviews() setUpLayout() } // MARK: - Subviews private func addSubviews() { // Add subviews } // MARK: - Layout private func setUpLayout() { // Set up constraints } // MARK: - Required initializer required init?(coder _: NSCoder) { nil } } @SzklarekMateusz Mobilization IX 2019 80
109. class DetailsView: UIView { let container: UIStackView = Subviews.container let verticalContainer: UIStackView = Subviews.verticalContainer let titleView: TitleView = TitleView() let separator: UIView = Subviews.separator let infoView: InfoView = InfoView() let icon: UIImageView = Views.imageView(contentMode: .scaleAspectFit) init() { super.init(frame: .zero) addSubviews() setUpLayout() apiService.getDetails { details in ... // present details } } ... @SzklarekMateusz Mobilization IX 2019 81
110. It's hard to reuse @SzklarekMateusz Mobilization IX 2019 82
111. class DetailsView: UIView { let container: UIStackView = Subviews.container let verticalContainer: UIStackView = Subviews.verticalContainer let titleView: TitleView = TitleView() let separator: UIView = Subviews.separator let infoView: InfoView = InfoView() let icon: UIImageView = Views.imageView(contentMode: .scaleAspectFit) init() { super.init(frame: .zero) addSubviews() setUpLayout() apiService.getDetails { details in ... // present details } } ... @SzklarekMateusz Mobilization IX 2019 83
112. Favourites statements @SzklarekMateusz Mobilization IX 2019 84
113. 1. "Get rid of Massive ViewController" @SzklarekMateusz Mobilization IX 2019 85
114. small View Controller + ... @SzklarekMateusz Mobilization IX 2019 86
115. small View Controller + massive View Model @SzklarekMateusz Mobilization IX 2019 87
116. "Extracting logic from VC to VM is nothing else than moving the Junk to a Different Drawer" @SzklarekMateusz Mobilization IX 2019 88
117. 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 Mobilization IX 2019 89
118. 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 Mobilization IX 2019 90
119. 2. "MVVM makes my apps more testable" @SzklarekMateusz Mobilization IX 2019 91
120. @SzklarekMateusz Mobilization IX 2019 92
121. 4 John: "We do MVVM because it's really easy to test our view models" @SzklarekMateusz Mobilization IX 2019 92
122. 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 Mobilization IX 2019 92
123. 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 Mobilization IX 2019 92
124. 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 Mobilization IX 2019 92
125. 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 Mobilization IX 2019 92
126. 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 Mobilization IX 2019 92
127. 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 Mobilization IX 2019 92
128. with MVVM more testable without MVVM less testable? @SzklarekMateusz Mobilization IX 2019 93
129. REALLY? @SzklarekMateusz Mobilization IX 2019 94
130. 3. "Because it's so popular and it's a perfect solution with RxSwift" @SzklarekMateusz Mobilization IX 2019 95
131. @SzklarekMateusz Mobilization IX 2019 96
132. Advantages @SzklarekMateusz Mobilization IX 2019 97
133. 4 nice way to keep the state of the view (simple struct) @SzklarekMateusz Mobilization IX 2019 98
134. struct BookViewModel { let id: String let name: String let author: String let coverImage: UIImage } @SzklarekMateusz Mobilization IX 2019 99
135. Disadvantages @SzklarekMateusz Mobilization IX 2019 100
136. Break SRP @SzklarekMateusz Mobilization IX 2019 101
137. Break SRP 4 Loading data from multiple APIs / endpoints @SzklarekMateusz Mobilization IX 2019 101
138. Break SRP 4 Loading data from multiple APIs / endpoints 4 Filtering data @SzklarekMateusz Mobilization IX 2019 101
139. Break SRP 4 Loading data from multiple APIs / endpoints 4 Filtering data 4 logic for formatting strings (composed from several other values) @SzklarekMateusz Mobilization IX 2019 101
140. 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 Mobilization IX 2019 101
141. 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 Mobilization IX 2019 101
142. 4 Break SRP 4 Poor reusability @SzklarekMateusz Mobilization IX 2019 102
143. 4 Break SRP 4 Poor reusability 4 Poor testability @SzklarekMateusz Mobilization IX 2019 103
144. 4 Break SRP 4 Poor reusability 4 Poor testability 4 without bindings it's still more code to write @SzklarekMateusz Mobilization IX 2019 104
145. 3 things to remember @SzklarekMateusz Mobilization IX 2019 105
146. 3 things to remember 4 architecture & design patterns are to solve problem not to create them @SzklarekMateusz Mobilization IX 2019 105
147. 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 Mobilization IX 2019 105
148. 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 Mobilization IX 2019 105
149. 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 Mobilization IX 2019 106
150. Mateusz Szklarek Senior iOS Developer @elpassion (Warsaw) mateuszszklarek @SzklarekMateusz @SzklarekMateusz Mobilization IX 2019 107