协议中关联类型的依赖倒置

Question

我很难尝试实现依赖倒置。环顾四周，找到一篇很棒的文章 Swift Type Erasure。我不确定如何才能在我的情况下获得优势。这就是我想要实现的目标。

网络协议

protocol Networkable {
    associatedtype Response: Decodable

    func request(handler: @escaping((Result<Response, Error>) -> ()))
}

Networkable 协议的具体实现

final class Networker<Response: Decodable>: Networkable {
    private let session: URLSession
    private let url: URL

    init(session: URLSession, url: URL) {
        self.session = session
        self.url = url
    }

    func request(handler: @escaping ((Result<Response, Error>) -> ())) {
        session.dataTask(with: url) { data, response, error in
            handler(.success(try! JSONDecoder().decode(Response.self, from: data!)))
        }
    }
}

依赖于Networkable协议的ViewModel

class ViewModel {
    let networker: Networkable
    // Error-> Protocol 'Networkable' can only be used as a generic constraint because it has Self or associated type requirements

    init(netwrorker: Networkable) {
        self.networker = netwrorker
    }

    func execute() {
        networker.request { _ in
            print("Responsed")
        }
    }
}

用法：

class View {
    let viewModel: ViewModel

    init() {
        let networker = Networker<ResponseModel>(session: .shared, url: URL(string: "SOME URL")!)
        self.viewModel = ViewModel(netwrorker: networker)
    }

    func load() {
        viewModel.execute()
    }
}

struct ResponseModel: Decodable {}

问题：

这是实现依赖倒置的正确方法吗？
如何在网络上实现通用行为 class 并且仍然开放测试？

Answer 1

您的 ViewModel class 格式错误：

class ViewModel<T: Decodable> {
    let networker: Networker<T>
    …
}

否则你可能会创建一个类型擦除的 AnyNetworkable 具体类型，你可以像这样使用它：

class ViewModel<T: Decodable> {
    let networker: AnyNetworkable<T>
    …
}

或者您可以采用更通用的方法，如：

class ViewModel<R, T: Networkable> where T.Response == R {
     let networker: T
}

显然，这同样反映在您的 View 类型上，您还需要针对 ViewModel.

的特定具体类型进行通用或专门化

协议中关联类型的依赖倒置

Dependency Inversion with assosiatedType in protocol

xcode

dependency-injection

swift

dependency-inversion