A journey from MVC to VIPER is a try to leverage different application architectures (as well as some concepts on top of MVC) to build more clean and readable software in Cocoa. Most of the described techniques can be successfully used while dealing with legacy codebase.

1. from MVC to VIPER
Krzysztof Profic
@kprofic

2. Legacy codebase
Better codebase

3. Pragmatic approach
what hurts my eyes?

4. Pragmatic approach
what hurts my eyes?
UIViewController

5. Massive
UIViewController

6. 4 Steps
• MVC on diet
• MVVM
• Intentions
• VIPER

7. 4 Steps
• MVC on diet
• MVVM
• Intentions
• VIPER

8. MVC on diet
Massive View Controller
Light View Controller

9. Reducing
Massive ViewController
• extract datasource
• move domain logic into the model
• move view code into the view layer
objc.io #1

10. Reducing
Massive ViewController
• extract datasource
• move domain logic into the model
• move view code into the view layer
objc.io #1

11. Reducing
Massive ViewController
• extract datasource
• move domain logic into the model
• move view code into the view layer
objc.io #1

12. Reducing
Massive ViewController
• Separation of concerns
• Single responsibility principle
objc.io #1

13. Reanimate your MVC
reduce MVC principles violation
put ViewController on a diet

14. What is the Rule?

15. “Keep the code where
it belongs”

16. Layer

19. Controllers
Use Cases
Entities
Presenters
Gateways
UI
DB
External
Interfaces
Devices
The Clean Architecture
Enterprise Business Rules
Application Business Rules
Interface Adapters
Frameworks & Drivers
Web
Controller
Use Case
Interactor
Presenter
Use Case
Output Port
Use Case
Input Port
Flow of control
<I>
<I>
http://blog.8thlight.com

20. separation of concerns = dividing software into …
Layers

21. “Keep the code on
the right layer”

22. The Dependency Rule

23. Controllers
Use Cases
Entities
Presenters
Gateways
UI
DB
External
Interfaces
Devices
The Clean Architecture
Enterprise Business Rules
Application Business Rules
Interface Adapters
Frameworks & Drivers
Web
Controller
Use Case
Interactor
Presenter
Use Case
Output Port
Use Case
Input Port
Flow of control
<I>
<I>
http://blog.8thlight.com

24. MVC variation

25. MVC variation

26. MVVM

27. 4 Steps
• MVC on diet
• MVVM
• Intentions
• VIPER

28. Let’s talk code

29. - (void)viewDidLoad {
[super viewDidLoad];
if (self.model.salutation.length > 0) {
self.nameLabel.text = [NSString stringWithFormat:@"%@ %@ %@“,
self.model.salutation,
self.model.firstName,
self.model.lastName];
} else {
self.nameLabel.text = [NSString stringWithFormat:@"%@ %@“,
self.model.firstName,
self.model.lastName];
}
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"EEEE MMMM d, yyyy"];
self.birthdateLabel.text = [dateFormatter
stringFromDate:model.birthdate];
}
PersonViewController.m

30. @implementation PersonViewModel
- (instancetype)initWithPerson:(Person *)person {
self = [super init];
if (!self) return nil;
_person = person;
if (person.salutation.length > 0) {
_nameText = [NSString stringWithFormat:@"%@ %@ %@“,
self.person.salutation,
self.person.firstName, self.person.lastName];
} else {
_nameText = [NSString stringWithFormat:@"%@ %@",
self.person.firstName,
self.person.lastName];
}
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"EEEE MMMM d, yyyy"];
_birthdateText = [dateFormatter
stringFromDate:person.birthdate];
return self;
}
@end PersonViewModel.m

31. - (void)viewDidLoad {
[super viewDidLoad];
self.nameLabel.text = self.viewModel.nameText;
self.birthdateLabel.text = self.viewModel.birthdateText;
}
PersonViewController.m

32. 4 Steps
• MVC on diet
• MVVM
• Intentions
• VIPER

33. Motivation
• ViewController implements only viewWill* viewDid*

34. • encapsulate small pieces of business logic
• use case approach (form validation, login user)
• hookable via &
• reusable
Intentions
Architecture is about Intent “Uncle Bob”
IBOutlet IBAction

36. @interface ViewController ()
@property (strong) IBOutlet ModelContainer* modelContainer;
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
PersonViewModel * pvm = [[PersonViewModel alloc]
initWithModel:self.person];
self.modelContainer.viewModel = pvm;
}
@end
ViewController.m

37. Observing ViewModel

38. @interface ObserveIntention ()
@property (strong, nonatomic) IBOutlet id sourceObject;
@property (strong, nonatomic) IBOutlet id target;
@property (copy, nonatomic) IBOutlet NSString *sourceKeyPath;
@property (copy, nonatomic) IBOutlet NSString *targetKeyPath;
@end

39. @implementation ObserveIntention
- (void)awakeFromNib {
[super awakeFromNib];
[self updateValue];
[self.sourceObject addObserver:self
forKeyPath:self.sourceKeyPath options:0 context:nil];
}
- (void)updateValue {
id value = [self.sourceObject valueForKeyPath:
self.sourceKeyPath];
if (self.targetKeyPath) {
[self.target setValue:value forKeyPath:self.targetKeyPath];
}
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)obj
change:(NSDictionary *)change context:(void *)context {
if ([keyPath isEqualToString:self.sourceKeyPath]) {
[self updateValue];
}
}
@end

41. Behaviours
UIControl
objc.io #13

42. Login

43. User Story #90.10 - Login
• A. When I as a user open the app the first time I
enter the “main login” page, where I need to login
with my username (email address) and password.
• B. When I tap the “login button” while online and no
errors occur I’m moved to initial page with users
profile.

44. User Story #90.10 - Login
• A. When I as a user open the app the first time I
enter the “main login” page, where I need to login
with my username (email address) and password.
• B. When I tap the “login button” while online and
no errors occur I’m moved to initial page with users
profile.

46. @interface LoginIntention()
@property (strong) IBOutlet UITextField * usernameTextField;
@property (strong) IBOutlet UITextField * passwordTextField;
@property (strong, nonatomic) IBOutlet UILabel * statusLabel;
@end
@implementation LoginIntention
- (IBAction)login:(id)sender {
self.statusLabel.text = @"connecting...";
[self sendActionsForControlEvents:UIControlEventValueChanged];
self.statusLabel.text = [NSString
stringWithFormat:@"Authenticating %@“,
self.usernameTextField.text];
[self sendActionsForControlEvents:UIControlEventValueChanged];
self.statusLabel.text = @"done";
[self sendActionsForControlEvents:UIControlEventValueChanged];
}
@end
LoginIntention.m

47. @implementation LoginViewController
- (IBAction)loginIntentionStateChanged:(LoginIntention *)sender {
if ([sender.statusLabel.text isEqualToString:@"done"]){
[self.presentingViewController
dismissViewControllerAnimated:YES completion:nil];
}
}
@end
LoginViewController.m

48. 4 Steps
• MVC on diet
• MVVM
• Intentions
• VIPER

49. If you want more, checkout
VIPER
• View
• Interactor
• Presenter
• Entity
• Routing

50. Summary:
MVC on diet
MVVM
Intentions / Behaviours
VIPER

51. Thank you!
Krzysztof Profic
@kprofic

52. • http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-
architecture.html
• http://www.scottlogic.com/blog/2014/05/11/
reactivecocoa-tableview-binding.html
• http://chris.eidhof.nl/posts/intentions.html
• http://www.objc.io/issue-13/behaviors.html
• http://www.objc.io/issue-13/viper.html