From mvc to viper

from MVC to VIPER
Krzysztof Profic
@kprofic

Legacy codebase
Better codebase

Pragmatic approach
what hurts my eyes?

Pragmatic approach
what hurts my eyes?
UIViewController

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

MVC on diet
Massive View Controller
Light View Controller

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

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

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

“Keep the code where
it belongs”

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

separation of concerns = dividing software into …
Layers

“Keep the code on
the right layer”

- (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

@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

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

Motivation
• ViewController implements only viewWill* viewDid*

• 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

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

@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

@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

Behaviours
UIControl
objc.io #13

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.

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.

@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.statusLabel.text = @"done";
}
@end
LoginIntention.m

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

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

Summary:
MVC on diet
MVVM
Intentions / Behaviours
VIPER

Thank you!
Krzysztof Profic
@kprofic

• 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

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