swift - 使用泛型将额外的 props 注入(inject)到 View 模型中

Question

已关注 this blog post我在我的应用程序中创建了一个 MVVM 模式。

我有以下内容 -

protocol ViewModelType {
    associatedtype Dependency
    associatedtype Bindings

    init(dependency: Dependency, bindings: Bindings)
}

enum Attachable<VM: ViewModelType> {

    case detached(VM.Dependency)
    case attached(VM.Dependency, VM)

    mutating func bind(_ bindings: VM.Bindings) -> VM {
        switch self {
        case let .detached(dependency):
            let vm = VM(dependency: dependency, bindings: bindings)
            self = .attached(dependency, vm)
            return vm
        case let .attached(dependency, _):
            let vm = VM(dependency: dependency, bindings: bindings)
            self = .attached(dependency, vm)
            return vm
        }
    }
}

View Controller

final class StartViewController: BaseViewController<StartView> {

    var viewModel: Attachable<StartViewModel>!
    var bindings: StartViewModel.Bindings {

        let viewWillAppear = rx.sentMessage(#selector(UIViewController.viewWillAppear))
            .mapToVoid()
            .asDriverOnErrorJustComplete()

        return StartViewModel.Bindings(
            checkAuthState: viewWillAppear
        )
    }
}

extension StartViewController: ViewModelAttaching {
    func bind(viewModel: StartViewModel) -> StartViewModel {
        return viewModel
    }
}

View 模型

final class StartViewModel: ViewModelType {

    typealias Dependency = HasAuthService

    let authCheck: Driver<Void>

    struct Bindings {
        let checkAuthState: Driver<Void>
    }

    private let disposeBag = DisposeBag()

    init(dependency: Dependency, bindings: Bindings) {

        authCheck = bindings.checkAuthState
            .flatMap {
                return dependency.authSvc.checkSession()
                .mapToVoid()
                .asDriver(onErrorJustReturn: ())
        }
    }
}

这允许我按如下方式设置我的 View -

        let viewController = StartViewController()
        let avm: Attachable<StartViewModel> = .detached(dependencies)
        let viewModel = viewController.attach(wrapper: avm)

        navigationController.setViewControllers([viewController], animated: false)

这很好用，非常容易测试，我对它的工作方式很满意。然而，我有一个场景，我需要将一些额外的 Prop 传递到我的 ViewModel 中。 。

例如，userId在个人资料场景的情况下。

此模式保留 init方法，所以我需要一种通过 .detached(dependencies) 注入(inject)额外 Prop 的方法

类似于 .detached(dependencies, userId)但是我不确定如何以通用方式执行此操作。

我已经尝试过 - 注意添加 Props和props

protocol ViewModelType {
    associatedtype Dependency
    associatedtype Bindings
    associatedtype Props

    init(dependency: Dependency, bindings: Bindings, props: Props?)
}

enum Attachable<VM: ViewModelType> {

    case detached(VM.Dependency, VM.Props)
    case attached(VM.Dependency, VM, VM.Props)

    mutating func bind(_ bindings: VM.Bindings) -> VM {
        switch self {
        case let .detached(dependency, props):
            let vm = VM(dependency: dependency, bindings: bindings, props: props)
            self = .attached(dependency, vm, props)
            return vm
        case let .attached(dependency, _, props):
            let vm = VM(dependency: dependency, bindings: bindings, props: props)
            self = .attached(dependency, vm, props)
            return vm
        }
    }
}

但这需要我更新我的 ViewModel与以下 -

**ViewModel**
```swift
typealias Props = <Some Prop Type>
init(dependency: Dependency, bindings: Bindings, props: Props?)

这非常有效，除非我不需要注入(inject)任何 Prop 。然后我陷入了需要为未使用的东西指定类型的困境。

我已经尝试过了 -

typealias Props = Void?
init(dependency: Dependency, bindings: Bindings, props: Props?)

然后用 -

设置我的 View

let avm: Attachable<StartViewModel> = .detached(dependencies, nil)

但必须添加typealias Props = Void?在我所有不接受任何东西的模型中，感觉不太好

如何以最具扩展性、通用的方式实现这一目标？

Answer 1

与其引入 Props，为什么不将附加信息隐藏在 Dependency 后面呢？例如，在您的情况下，您可以:

final class ProfileViewModel: ViewModelType {

    let authCheck: Driver<Void>

    struct Dependency {
        let authSvc: HasAuthService
        let userId: String
    }

    struct Bindings {
        let checkAuthState: Driver<Void>
    }

    private let disposeBag = DisposeBag()

    init(dependency: Dependency, bindings: Bindings) {

        authCheck = bindings.checkAuthState
            .flatMap {
                return dependency.authSvc.checkSession()
                .mapToVoid()
                .asDriver(onErrorJustReturn: ())
        }

        // use dependency.userId
    }
}