The first question after people have learned about how to implement anadvanced architecture in their applications from scratch is: "How do I transform my codebase from its current state to a well architected app?" Forget about BigBang rewrites. Come and learn some strategies, tricks, and gotchas about how to do the migration to an advanced arch mobile app. Move to from Objective-C to Swift in the process and keep it functional during the whole process.

1. Refactor Your
Way Forward
Jorge D. Ortiz-Fuentes
@jdortiz

2. A Canonical
Examples
Production

3. #AdvArchMobile
Agenda
★ The challenge
★ Strategy
★ Tactics
★ Recap

4. The
Challenge

5. #AdvArchMobile
Sounds familiar?
★ Legacy application
• No tests
• Outdated
★ Written in Objective-C
★ Not (m)any tests
★ Multiple styles and ways to do things
★ Not much info from the previous developer

6. #AdvArchMobile
Need a Better
Architecture
★ Difficult to add new features without
breaking existing ones
★ Difficult to find and solve bugs
★ Expensive to maintain
★ Difficult to add tests

7. #AdvArchMobile
My Example
★ App: OpenIt
★ Credit: Patrick Balestra
★ Thanks!
★ Great code for an example
★ All criticism IS constructive

8. Strategy

9. Ideas to Enhance

10. Persistance FW
View
Network
LocationFW
Presenter
Entity Gateway
Clean Architecture
Interactor
Entity

11. Clean Architecture: iOS
App
Delegate
View (VC) Presenter Interactor
Entity
Gateway
Connector

12. #AdvArchMobile
Goals
★ New feature: Apple rating API
★ Don’t break anything
★ Enhance when possible

13. No Big Bang Rewrite
Still love the TV series

14. Information
Gathering

15. – Sun Tzu
“Know your enemy and know yourself and
you can fight a hundred battles without
disaster.”

16. Pragmatic Information
Gathering
Make it Work

17. #AdvArchMobile
Make it Work
★ Install dependencies
• Pods/Carthage, if any
• API keys
★ Build
★ Fix big problems until it works

18. #AdvArchMobile
Make it Work
★ DON’T update the project settings yet
★ DON’T add any functionality yet
★ DON’T fix any other bugs yet

19. Commit!

20. #AdvArchMobile
Explore the Battlefield
★ Take a glimpse a the code
★ Tests? Runnable? Pass?
★ Documentation?
★ Oral transmission?
★ Business goals

21. #AdvArchMobile
Design your strategy
★ Planed features
★ Pain points

22. #AdvArchMobile
Main Strategic
Approaches
★ From the model upwards
• Less intuitive
• Still requires injections from top to bottom
★ From the views inwards
• More work initially

23. #AdvArchMobile
Shape the Strategy
★ App delegate: Size? Relevant tasks? Easy to
replace (And remove main.m)?
★ Storyboards?
★ Tests coverage? Only for the model?
★ Frameworks used (Persistence & others)?
★ DI? Abstractions for DIP?
★ VCs screaming for changes?

24. But remember
Only small non breaking changes allowed

25. Tactics

26. Add Tests

27. #AdvArchMobile
Add Tests
★ Set up the testing target
★ Language is Swift
★ Start with main target
★ Don't add others (frameworks) until required
★ Cmd+U To test that it works.
★ Delete the default tests

28. Commit!

29. Zero Visibility
Here Be Dragons

30. Use the Tools

31. #AdvArchMobile
Proper Git
★ Branch often
★ Better, git flow: Feature branch for each
part of migration
★ Avoid long lived branches
★ Use branch by abstraction instead

32. #AdvArchMobile
Branch by Abstraction
2 1
1
1 2

33. #AdvArchMobile
Use Xcode Groups
★ Put all legacy code in a group
★ Support files and assets in another one
★ Create new Groups (or folders) to organize
new code

34. Use Xcode Refactor
Feature

35. 😂

36. Replace App
Delegate (& main.m)

37. #AdvArchMobile
Very Simple (when it is)
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
}

38. Commit!

39. Enable Dependency
Injection

40. #AdvArchMobile
Introduce DI
from Root VC
★ Change behavior in Info.plist
★ App delegate creates initial view controller
★ Pass into a dumb (yet) connector
★ Add Bridging header

41. #AdvArchMobile
Info.plist

42. Commit!

43. View Controller Talks
to Dumb Presenter

44. Mark Connection Points

45. #AdvArchMobile
Introduce Presenter
★ @objc
★ Pass events
★ Test VC
★ Generate a skeleton for the presenter

46. #AdvArchMobile
Cheat to keep it working
- (NSInteger)tableView:(UITableView *)tableView
numberOfRowsInSection:(NSInteger)section {
// DONE: Invoke presenter numberOfActions
NSInteger rows = self.presenter.numberOfActions;
// TODO: Remove when using real presenter
if (rows < 0) {
rows = self.actions.count;
}
return rows;
}

47. #AdvArchMobile
Cheat to provide
dependencies
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath {
// DONE: Invoke presenter configure(cell:forRow:)
UITableViewCell *cell = [tableView
dequeueReusableCellWithIdentifier:@"cell" forIndexPath:indexPath];
// TODO: In the new view replace with the actual cell
[self.presenter configureWithCell:[[ActionTableViewCell alloc]
init] atRow:indexPath.row];
cell.textLabel.text = self.actions[indexPath.row][0][@"Title"];
cell.detailTextLabel.text = self.actions[indexPath.row][1]
[@"Type"];
cell.imageView.image = [UIImage
imageNamed:self.actions[indexPath.row][1][@"Type"]];
return cell;
}

48. Commit!

49. Refactor Persistence

50. #AdvArchMobile
- (void)viewDidLoad {
[super viewDidLoad];
[self.presenter viewReady];
// …
self.actions = [self
fetchActions];
// …
}
- (NSMutableArray *) fetchActions
{
return [[NSMutableArray alloc]
initWithArray:[[NSUserDefaults
standardUserDefaults]
objectForKey:@"actions"]];
}
Extract Methods with
Persistence
- (void)viewDidLoad {
[super viewDidLoad];
[self.presenter
viewReady];
// …
self.actions =
[[NSMutableArray alloc]
initWithArray:
[[NSUserDefaults
standardUserDefaults]
objectForKey:@"actions"]];
// …
}

51. #AdvArchMobile
And Test It
func testFetchActionsObtainsDataFromUserDefaults() {
let userDefaultsMock = UserDefaultsMock()
sut.setValue(userDefaultsMock, forKey: "userDefaults")
_ = sut.fetchActions()
XCTAssertTrue(userDefaultsMock.objectForKeyInvoked)
}

52. Commit!

53. Get the new VC in

54. #AdvArchMobile
New Swift VC
★ Replaces the old one
★ Refactor Storyboard
★ New Swift class with the desired name
★ Reuse the tests to create an instance of this
one

55. Refactor the Storyboard

56. Deal with
Limitations

57. #AdvArchMobile
Rough Edges
★ Structs & Enums
★ Tuples
★ Generics
★ Curried & global functions
★ Typealiases

58. #AdvArchMobile
@objcMembers class ActionWrapper: NSObject
{
private var action: Action
var title: String {
get {
return action.title
}
set(newTitle) {
action.title = newTitle
}
}
//…
init(action: Action) {
self.action = action
}
init(title: String, type: String, url:
String) {
action = Action(title: title,
type: type, url: url)
}
}
Use Wrappers
struct Action {
var title: String
var type: String
var url: String
}

59. Commit!

60. #AdvArchMobile
But…
★ Entity Gateway should implement both
★ Value semantics are lost
★ Use scarcely
★ Remove when possible

61. And Finally…
New Use Case

62. #AdvArchMobile
Use Case
typealias AskForRatingCompletion = (Bool) -> ()
class AskForRatingUseCase: UseCase {
let entityGateway: EntityGateway
let preferencesGateway: PreferencesGateway
let completion: AskForRatingCompletion
init(entityGateway: EntityGateway, preferencesGateway:
PreferencesGateway,
completion: @escaping AskForRatingCompletion) {
self.entityGateway = entityGateway
self.preferencesGateway = preferencesGateway
self.completion = completion
}
func execute() {
let ask = entityGateway.numberOfActions > 10
&& preferencesGateway.daysSinceLastRating > 180
completion(ask)
}
}

63. #AdvArchMobile
// View (extension)
func askForRating() {
SKStoreReviewController.requestRe
view()
}
Presenter & View
// Presenter
func viewReady() {
actions = fetchActions()
mayAskUserForRating()
}
private func
mayAskUserForRating() {
let useCase =
useCaseFactory.askForRatingUseCas
e(completion: { (shouldAsk: Bool)
in
view.askForRating()
})
useCase.execute()
}

64. Commit!

65. Recap

66. #AdvArchMobile
Recap
★ Incremental refactoring is feasible
★ Design your strategy
★ Use the tactics
★ Small non breaking changes are best
★ Tests are key
★ Don’t follow sequential order

67. Tusen
Takk!

68. Thank
You!

69. @jdortiz
#AdvArchMobile