The right way to write providers for VIPER?

I can think about that you just simply began to put in writing your first VIPER module and also you may marvel: the place ought to I put all my community communication, CoreLocation, CoreData or “no matter service” code, that is not associated to the consumer interface in any respect?

To the service layer!

I normally name these the API, location, storage as a service, as a result of they serve your modules with some form of data. Plus they’ll encapsulate the underlying layer, offering a well-defined API interface on your VIPER modules. 😅

Okay, however what about interactors? Should not I implement this sort of stuff there?

Nicely, my reply isn’t any, as a result of there’s a main distinction between providers and interactors. Whereas a service is only a “dummy” wrapper arund e.g. a RESTful API, one other one across the CoreData storage, an interactor nevertheless may use each of them to request some form of knowledge although the API, and put it aside domestically utilizing the storage service. Interactors may also do sorting, filtering, transformation between Knowledge Switch Objects (DTOs) and entities, extra about them later.

Sufficient concept for now, let’s create a brand new service.

Service interfaces

This time because the Protocol Goal Programming paradigm says:

We begin designing our system by defining protocols.

Our first one goes to be a extremely easy one for all of the providers:

protocol ServiceInterface: class {
    func setup()
}

extension ServiceInterface {

    func setup() {
        
    }
}

The setup will likely be referred to as for every service through the service initialization course of. We will lengthen the bottom service so we do not have to implement this methodology, however provided that we actually need to do one thing, like establishing our CoreData stack.

Subsequent we are able to give you our API service, on this case I’ll implement a dummy endpoint that hundreds some knowledge utilizing the brand new Mix framework with URLSession, however after all you possibly can go together with completion blocks or Guarantees as nicely.

protocol ApiServiceInterface: ServiceInterface {

    func todos() -> AnyPublisher<[TodoObject], HTTP.Error>
}

These days I am utilizing a HTTP namespace for all my community associated stuff, like request strategies, responses, errors, and many others. Be at liberty to increase it primarily based in your wants.

enum HTTP {

    enum Technique: String {
        case get
        
    }
    enum Error: LocalizedError {
        case invalidResponse
        case statusCode(Int)
        case unknown(Swift.Error)
    }
}

As you possibly can see it is fairly light-weight, however it’s extraordinarily useful. We have not talked in regards to the TodoObject but. That is going to be our very first DTO. 😱

Knowledge Switch Objects

A knowledge switch object (DTO) is an object that carries knowledge between processes. – wikipedia

On this case we’re not speaking about processes, however providers & VIPER modules. They exists so we are able to decouple our service layer from our modules. The interactor can remodel the DTO right into a module entity, so all different elements of the VIPER module will likely be fully impartial from the service. Price to say {that a} DTO is normally actually easy, in a RESTful API service, a DTO can implement the Codable interface and nothing extra or for CoreData it may be only a NSManagedObject subclass.

struct TodoObject: Codable {
    let id: Int
    let title: String
    let accomplished: Bool
}

You may also use a easy DTO to wrap your request parameters. For instance you need to use a TodoRequestObject which might comprise some filter or sorting parameters. You may seen that I all the time use the Object suffix for my DTO’s, that is a private choice, however it helps me differentiate them from entities.

Going somewhat bit additional this manner: you possibly can publish your whole service layer as an encapsulated Swift bundle utilizing SPM, from Xcode 11 these packages are natively supported so should you’re nonetheless utilizing CocoaPods, it is best to take into account migrating to the Swift Package deal Supervisor as quickly as potential.

Service implementations

Earlier than we begin constructing our actual service implementation, it is good to have a pretend one for demos or testing functions. I name this pretend, as a result of we’ll return a set quantity of pretend knowledge, however it’s near our real-world implementation. If our request would come with filtering or sorting, then this pretend implementation service ought to filter or type our response like the ultimate one would do it.

ultimate class FakeApiService: ApiServiceInterface {

    var delay: TimeInterval

    init(delay: TimeInterval = 1) {
        self.delay = delay
    }

    non-public func fakeRequest<T>(response: T) -> AnyPublisher<T, HTTP.Error> {
        return Future<T, HTTP.Error> { promise in
            promise(.success(response))
        }
        .delay(for: .init(self.delay), scheduler: RunLoop.important)
        .eraseToAnyPublisher()
    }

    func todos() -> AnyPublisher<[TodoObject], HTTP.Error> {
        let todos = [
            TodoObject(id: 1, title: "first", completed: false),
            TodoObject(id: 2, title: "second", completed: false),
            TodoObject(id: 3, title: "third", completed: false),
        ]
        return self.fakeRequest(response: todos)
    }
}

I like so as to add some delay to my pretend objects, as a result of it helps me testing the UI stack. I am a giant fan of Scott’s repair a nasty consumer interface article. You need to positively learn it, as a result of it is superb and it’ll enable you to design higher merchandise. 👍

Transferring ahead, right here is the precise “real-world” implementation of the service:

ultimate class MyApiService: ApiServiceInterface {

    let baseUrl: String

    init(baseUrl: String) {
        self.baseUrl = baseUrl
    }

    func todos() -> AnyPublisher<[TodoObject], HTTP.Error> {
        let url = URL(string: self.baseUrl + "todos")!
        var request = URLRequest(url: url)
        request.httpMethod = HTTP.Technique.get.rawValue.uppercased()

        return URLSession.shared.dataTaskPublisher(for: request)
        .tryMap { knowledge, response in
            guard let httpResponse = response as? HTTPURLResponse else {
                throw HTTP.Error.invalidResponse
            }
            guard httpResponse.statusCode == 200 else {
                throw HTTP.Error.statusCode(httpResponse.statusCode)
            }
            return knowledge
        }
        .decode(sort: [TodoObject].self, decoder: JSONDecoder())
        .mapError { error -> HTTP.Error in
            if let httpError = error as? HTTP.Error {
                return httpError
            }
            return HTTP.Error.unknown(error)
        }
        .eraseToAnyPublisher()
    }
}

The factor is that we may make this even higher, however for the sake of simplicity I’ll “hack-together” the implementation. I do not just like the implicitly unwrapped url, and lots of extra little particulars, however for studying functions it’s very positive. 😛

So the massive query is now, put issues togehter? I imply we have now a working service implementation, a pretend service implementation, however how the hell ought to we put every thing into an actual Xcode venture, with out transport pretend code into manufacturing?

Goal environments

Normally you’ll have a dwell manufacturing surroundings, a growth surroundings, perhaps a staging surroundings and a few extra for QA, UAT, or demo functions. Issues can fluctuate for these environments similar to the ultimate API url or the app icon, and many others.

This time I’ll arrange a venture with 3 separate environments:

• Manufacturing
• Growth
• Faux

Should you begin with a brand new venture you will have one main (non-test) goal by default. You may duplicate a goal by right-clicking on it. Let’s do that two occasions.

I normally go together with a suffix for the goal and scheme names, aside from the manufacturing surroundings, the place I exploit the “base identify” with out the -Manufacturing postfix.

As you possibly can see on the screenshot I’ve a fundamental folder construction for the environments. There must be a separate Information.plist file for each goal, so I put them into the correct Property folder. The FakeApiService.swift is simply a part of the pretend goal, and each different file is shared. Wait, what the heck is a ServiceBuilder?

Dependency injection

A number of surroundings implies that we have now to make use of the appropriate service (or configuration) for each construct goal. I am utilizing the dependency injection design sample for this function. A service builder is only a protocol that helps to realize this purpose. It defines setup providers primarily based on the surroundings. Let me present you the way it works.

protocol ServiceBuilderInterface {

    var api: ApiServiceInterface { get }

    func setup()
}

extension ServiceBuilderInterface {

    func setup() {
        self.api.setup()
    }
}

Now for every goal (surroundings) I implement the ServiceBuilderInterface in an precise ServiceBuilder.swift file, so I can setup my providers simply as I want them.

ultimate class ServiceBuilder: ServiceBuilderInterface {

    lazy var api: ApiServiceInterface = {
        
        MyApiService(baseUrl: "https://jsonplaceholder.typicode.com")
    }()
}

I normally have a base service-interactor class that may obtain all of the providers through the initialization course of. So I can swap out something and not using a problem.

class ServiceInteractor {

    let providers: ServiceBuilderInterface

    init(providers: ServiceBuilderInterface = App.shared.providers) {
        self.providers = providers
    }
}

DI is nice, however I do not prefer to repeat myself an excessive amount of, that is why I am offering a default worth for this property, which is positioned in my solely singleton class referred to as App. I do know, singletons are evil, however I have already got an anti-pattern right here so it actually does not matter if I introduce another, proper? #bastard #singleton 🤔

ultimate class App {

    let providers = ServiceBuilder()

    

    static let shared = App()

    non-public init() {
        
    }

    

    func setup() {
        self.providers.setup()
    }
}

This setup is extraordinarily helpful if it involves testing. You may merely mock out all of the providers if you wish to check an interactor. It is also good and clear, as a result of you possibly can attain your strategies within the interactors like this: self.providers.api.todos()

You may apply the identical sample on your modules, I imply you possibly can have for instance a ModuleBuilder that implements a ModuleBuilderInterface and all of the routers can have them by means of DI, so you do not have to initialize every thing from scratch all of the tim utilizing the construct perform of the module. 😉

Nonetheless I need to make clear another factor…

Object, mannequin, entity, what the…?

A bit bit about naming conventions (I additionally use these as suffixes on a regular basis):

In my dictionary an Object is all the time a DTO, it solely lives within the service layer. It is a freakin dumb one, with none extra function than offering a pleasant Swiftish API. This implies you do not have to take care of JSON objects or something loopy like that, however you possibly can work instantly with these objects, which is normally a pleasant to have function.

An Entity is said to a VIPER module. Its function is to behave as a communication object that may be handed round between the view, interactor, presenter, router or as a parameter to a different module. It will possibly encapsulate the native stuff that is required for the module. This implies if one thing adjustments within the service layer (a DTO perhaps) your module will be capable to work, you solely need to align your interactor. 😬

Nonetheless, typically I am fully skipping entities, however I do know I should not. 🙁

A Mannequin refers to a view-model, which is a part of my part primarily based UI constructing method on prime of the UICollectionView class. You need to take a look at the hyperlinks if you wish to be taught extra about it, the syntax is similar to SwiftUI, however it’s clearly not as high-level. In abstract a mannequin all the time has the information that is required to render a view, nothing extra and nothing much less.

I hope this little article will enable you to construction your apps higher. VIPER may be fairly problematic typically, due to the best way it’s important to architect the apps. Utilizing these form of providers is a pleasant method to separate all of the completely different API connections, sensors, and lots of extra, and at last please keep in mind:

Not every thing is a VIPER module.

You may obtain the supply recordsdata for this text utilizing The.Swift.Dev tutorials repository on GitHub. Thanks for studying, if you have not finished it but please subscribe to my e-newsletter beneath, or ship me concepts, feedbacks by means of twitter. 👏