协议内部的Swift协议

Question

我遇到了Swift协议的问题。我有这样的事情：

protocol OnboardingPage {
  var viewModel: OnboardingPageViewModel! { get }
}

protocol OnboardingPageViewModel {
  func getValue() -> Bool
}

// ---

class FirstNameViewController: UIViewController, OnboardingPage {
  var viewModel: FirstNameViewModel!
}

class FirstNameViewModel: OnboardingPageViewModel {
  func getValue() -> Bool {
    return true
  }
}

class GenderViewController: UIViewController, OnboardingPage {
  var viewModel: GenderViewModel!
}

class GenderViewModel: OnboardingPageViewModel {
  func getValue() -> Bool {
    return false
  }
}

我有大量的视图控制器来确认OnboardingPage协议，它们都有一个与OnboardingPageViewModel协议一致的视图模型。

但遗憾的是，上面的代码不起作用:它说FirstNameViewController不确认OnboardingPage协议，因为它的viewModel属性具有FirstNameViewModel而不是OnboardingPageViewModel类型--尽管FirstNameViewModel是一个OnboardingPageViewModel。

我怎么才能解决这个问题？

Answer 1

使用关联类型 OnboardingPageViewModel类型ViewModel

编辑的

protocol OnboardingPage {
    associatedtype ViewModel: OnboardingPageViewModel

    var viewModel: ViewModel { get }
}

protocol OnboardingPageViewModel {
    func getValue() -> Bool
}

class FirstNameViewController: OnboardingPage {
    let viewModel: FirstNameViewModel

    init(viewModel: FirstNameViewModel) {
        self.viewModel = viewModel
    }
}

class FirstNameViewModel: OnboardingPageViewModel {
    func getValue() -> Bool {
        return true
    }
}

class GenderViewController: OnboardingPage {
    let viewModel: GenderViewModel

    init(viewModel: GenderViewModel) {
        self.viewModel = viewModel
    }
}

class GenderViewModel: OnboardingPageViewModel {
    func getValue() -> Bool {
        return false
    }
}

Answer 2

您可以通过删除关联类型来解决页面数组issue：

protocol OnboardingPage {    
    var viewModel: OnboardingPageViewModel { get }
}

protocol OnboardingPageViewModel {
    func getValue() -> Bool
}

class FirstNameViewModel: OnboardingPageViewModel {
    func getValue() -> Bool {
        return true
    }
}

class FirstNameViewController: OnboardingPage {
    let viewModel: OnboardingPageViewModel

    init(viewModel: FirstNameViewModel) {
        self.viewModel = viewModel
    }
}

class GenderViewModel: OnboardingPageViewModel {
    func getValue() -> Bool {
        return false
    }
}

class GenderViewController: OnboardingPage {
    let viewModel: OnboardingPageViewModel

    init(viewModel: GenderViewModel) {
        self.viewModel = viewModel
    }
}

用法：

let nameModel = FirstNameViewModel()
let genderModel = GenderViewModel()

let array: [OnboardingPage] = [FirstNameViewController(viewModel: nameModel), GenderViewController(viewModel: genderModel)]

for page in array {
    print(page.viewModel.getValue())
}

但是，以这种方式，您的模型的具体类型将不能用于OnboardingPage一致性类的调用者。您可以尝试通过在OnboardingPage中实现访问者模式或增强其功能来解决这个问题。

当然，您可以使用Cruz示例编写let pages: [Any] = [FirstNameViewController(), GenderViewController()]，但是它很难看，如果可能的话，我强烈建议您不要在API中使用Any。