Being SOLID

MVVM, VIPER, MVC are quite different approaches to architecturing mobile applications. But they are based on several fundamental principles, like SOLID. Whatever architectural pattern you choose to use following these simple principles will help you write clean and maintainable code.

It's best to learn from mistakes. We are going to talk about each SOLID principle in the following way: "Violation of principle -> Discussion -> Refactoring". After this talk the audience should clearly understand how to apply SOLID principles to typical iOS development problems.

Transcript

1. Being SOLID Rambler&Co by Sergey Krapivenskiy @serkrapiv
2. (c) someone smart on the Internet “Do Not Learn Frameworks”
3. Fundamentals
4. Fundamentals Languages
5. Fundamentals Languages Frameworks
6. Fundamentals Languages Frameworks
7. RayWenderlich - driven development Senior ReactiveCocoa Developer Rambler worships VIPER
8. Fundamentals Languages Frameworks
9. Fundamentals Languages Frameworks
10. Fundamentals Languages Frameworks
11. Fundamentals • Data structures • Algorithms • Design patterns • DRY, KISS, YAGNI • SOLID • And a lot more
13. Single responsibility principle Open-closed principle Liskov substitution principle Interface segregation principle Dependency inversion principle
14. Single Responsibility Principle “A class should have only one reason to change”
15. MassiveViewController 1.Responsibilities are coupled 2.Hard to understand 3.Very hard to maintain
16. UITableViewController 1.Changing table logic 2.Changing UI or views hierarchy
17. UITableViewController Solution: don’t use this class
18. App launch Push notifications Quick actions Application state Open from URL Background tasks AppDelegate
19. App launch Push notifications Quick actions Application state Open from URL Background tasks AppDelegate
20. AppDelegate App launch Quick actions Spotlight Push notifications Open from URL App states Background tasks Handoff Extensions https://github.com/rambler-digital-solutions/RamblerAppDelegateProxy
21. SRP = reducing complexity
22. Single responsibility principle Open-closed principle Liskov substitution principle Interface segregation principle Dependency inversion principle
23. Open-Closed Principle “Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification”
24. Simple and stable design
25. News News News News
26. News News News News News with photo News with photo
27. News News News News News with photo News with photo Advertisement Advertisement
28. } else ... return cell; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView dequeue...]; id model = [self modelAtIndex:indexPath.row]; if ([model isKindOfClass:[News class]]) { NewsCell *newsCell = (NewsCell *)cell; [newsCell setupWithNews:model]; } else if ([model isKindOfClass:[Advertisement class]]) { AdvertisementCell *adCell = (AdvertisementCell *)cell; [adCell setupWithAd:model];
29. } else ... return cell; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView dequeue...]; id model = [self modelAtIndex:indexPath.row]; if ([model isKindOfClass:[News class]]) { NewsCell *newsCell = (NewsCell *)cell; [newsCell setupWithNews:model]; } else if ([model isKindOfClass:[Advertisement class]]) { AdvertisementCell *adCell = (AdvertisementCell *)cell; [adCell setupWithAd:model];
30. } else ... return cell; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView dequeue...]; id model = [self modelAtIndex:indexPath.row]; if ([model isKindOfClass:[News class]]) { NewsCell *newsCell = (NewsCell *)cell; [newsCell setupWithNews:model]; } else if ([model isKindOfClass:[Advertisement class]]) { AdvertisementCell *adCell = (AdvertisementCell *)cell; [adCell setupWithAd:model];
31. } else ... return cell; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView dequeue...]; id model = [self modelAtIndex:indexPath.row]; if ([model isKindOfClass:[News class]]) { NewsCell *newsCell = (NewsCell *)cell; [newsCell setupWithNews:model]; } else if ([model isKindOfClass:[Advertisement class]]) { AdvertisementCell *adCell = (AdvertisementCell *)cell; [adCell setupWithAd:model];
32. } else ... return cell; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView dequeue...]; id model = [self modelAtIndex:indexPath.row]; if ([model isKindOfClass:[News class]]) { NewsCell *newsCell = (NewsCell *)cell; [newsCell setupWithNews:model]; } else if ([model isKindOfClass:[Advertisement class]]) { AdvertisementCell *adCell = (AdvertisementCell *)cell; [adCell setupWithAd:model];
34. - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { id model = [self modelAtIndex:indexPath.row]; UITableViewCell<ConfigurableCell> *cell = ...; [cell configureWithObject:model]; return cell; }
35. NewsCell PhotoCell AdCell <ConfigurableCell> - (void)configure:(<CellObject>)object; - (Class)cellClass;
36. <ConfigurableCell> - (void)configure:(<CellObject>)object; News Photo Advert <CellObject> - (Class)cellClass;
37. <ConfigurableCell> - (void)configure:(<CellObject>)object; <CellObject> - (Class)cellClass;
38. When should we use it?
40. Single responsibility principle Open-closed principle Liskov substitution principle Interface segregation principle Dependency inversion principle
42. Liskov Substitution Principle “Subtypes must be substitutable for their base types”
43. Used to check if we use inheritance correctly
44. - (void)hideViews { [UIView animateWithDuration:1.0 animations:^ { for (UIView *view in self.animatableViews) { view.alpha = 0.5f; } }]; }
45. UIView UIVisualEffectView Looks fine ! <UIVisualEffectView> is being asked to animate its opacity. This will cause the effect to appear broken until opacity returns to 1
46. UIView UIVisualEffectView Looks fine ! <UIVisualEffectView> is being asked to animate its opacity. This will cause the effect to appear broken until opacity returns to 1
47. UIView UIVisualEffectView Looks fine ! <UIVisualEffectView> is being asked to animate its opacity. This will cause the effect to appear broken until opacity returns to 1
48. ¯\_(ϑ)_/¯
49. Single responsibility principle Open-closed principle Liskov substitution principle Interface segregation principle Dependency inversion principle
50. Interface Segregation Principle “Clients should not be forced to depend on methods that they do not use”
51. MailAPIClient - auth - findContact - getMailboxes - createMailbox - sendMail
52. MailAPIClient - auth - findContact - getMailboxes - createMailbox - sendMail Auth Contacts Mailboxes Messages
53. MailAPIClient - auth - findContact - getMailboxes - createMailbox - sendMail Auth Contacts Mailboxes Messages - auth - findContact - getMailboxes - createMailbox - sendMail - auth - findContact - getMailboxes - createMailbox - sendMail - auth - findContact - getMailboxes - createMailbox - sendMail - auth - findContact - getMailboxes - createMailbox - sendMail
54. AuthService MailboxService ContactService MessageService Auth Contacts Mailboxes Messages - auth - findContact - getMailboxes - createMailbox - sendMail - auth - findContact - getMailboxes - createMailbox - sendMail - auth - findContact - getMailboxes - createMailbox - sendMail - auth - findContact - getMailboxes - createMailbox - sendMail MailAPIClient
55. ISP is not SRP
56. - sendSelfDestructMessage - deleteBothMessages ChatChannel - loadMessages - sendMessage - replyToMessage - forwardMessage - banUser - pinMessage
57. - sendSelfDestructMessage - deleteBothMessages ChatChannel - loadMessages - sendMessage - replyToMessage - forwardMessage Channel SecretChat Supergroup - banUser Group - pinMessage
58. - sendSelfDestructMessage - deleteBothMessages ChatChannel - loadMessages - sendMessage - replyToMessage - forwardMessage Channel SecretChat Supergroup - banUser Group - loadMessages - sendMessage - replyToMessage - forwardMessage - sendSelfDestruct - deleteBoth - pinMessage - banUser - pinMessage - loadMessages - sendMessage - replyToMessage - forwardMessage - sendSelfDestruct - deleteBoth - pinMessage - banUser - loadMessages - sendMessage - replyToMessage - forwardMessage - sendSelfDestruct - deleteBoth - pinMessage - banUser - loadMessages - sendMessage - replyToMessage - forwardMessage - sendSelfDestruct - deleteBoth - pinMessage - banUser
59. Single responsibility principle Open-closed principle Liskov substitution principle Interface segregation principle Dependency inversion principle
60. Dependency Inversion Principle “A. High-level modules should not depend on low-level modules. Both should depend on abstractions”
61. Dependency Inversion Principle “B. Abstractions should not depend on details. Details should depend on abstractions”
62. - (void)displayNews { NSPredicate *newsPredicate = ...; NSArray *news = [News MR_findAllWithPredicate:newsPredicate]; // Show news } Depending on Core Data
63. NewsViewController MagicalRecord "
64. NewsViewController MagicalRecord Realm "
65. NewsViewController MagicalRecord Realm "
66. @protocol NewsProvider <NSObject> - (NSArray *)obtainNewsForDate:(NSDate *)date; @end Depending on abstraction - (void)displayNews { NSDate *todayDate = ...; NSArray *news = [self.newsProvider obtainNewsForDate:todayDate]; // Show news }
67. @protocol NewsProvider <NSObject> - (NSArray *)obtainNewsForDate:(NSDate *)date; @end Depending on abstraction - (void)displayNews { NSDate *todayDate = ...; NSArray *news = [self.newsProvider obtainNewsForDate:todayDate]; // Show news }
68. @interface NewsViewController : UIViewController - (instancetype)initWithNewsProvider:(id<NewsProvider>)newsProvider; @end Depending on abstraction
69. NewsViewController <NewsProvider> MagicalRecord NewsProvider
70. NewsViewController <NewsProvider> Realm NewsProvider
71. Dependencies are inverted #
72. There is no silver bullet $
73. - Bruce Lee “Obey the principles without being bound by them”