VIPER Example

Presentation Logic

• View - delegates user interaction events to the Presenter and displays data passed by the Presenter
• All UIViewController, UIView, UITableViewCell subclasses belong to the View layer
• Usually the view is passive / dumb - it shouldn't contain any complex logic
• Presenter - contains the presentation logic and tells the View what to present
• Usually we have one Presenter per scene (view controller)
• It doesn't reference the concrete type of the View, but rather it references the View protocol that is implemented usually by a UIViewController subclass
• It should be a plain Objective-c class and not reference any iOS framework classes - this makes it easier to reuse
• Configurator/Assembly - injects the dependency object graph into the scene (view controller)
• You could very easily use a DI (dependency injection) library. Typhoon is used here.
• Router - contains navigation / flow logic from one scene (view controller) to another
• In some communities / blog posts it might be referred to as a FlowController
• It is usually referenced only by the Presenter

Business Logic

• UseCase / Interactor - contains the application / business logic for a specific use case in your application
• It is referenced by the Presenter. The Presenter can reference multiple UseCases since it's common to have multiple use cases on the same screen
• It manipulates Entities and communicates with Gateways to retrieve / persist the entities
• The Gateway protocols should be defined in the Application Logic layers and implemented by the Gateways & Framework Logic
• The separation described above ensures that the Application Logic depends on abstractions and not on actual frameworks / implementations
• Entity - plain ``Objective-C` classes
• Models objects used by your application such as Order, Product, Shopping Cart, etc

Gateways & Framework Logic

• Gateway - contains actual implementation of the protocols defined in the Application Logic layer
• We can implement for instance a LocalPersistenceGateway protocol using CoreData, Realm, Sqlite, or even simple use file system
• We can implement for instance an ApiGateway protocol using URLSession, AFNetworking or other.
• We can implement for instance a UserSettings protocol using UserDefaults
• Persistence / API Entities - contains framework specific representations
• Framework specific APIs - contains implementations of iOS specific APIs such as sensors / bluetooth / camera

Test

• Specta used for Unit testing