冗余约束'Self'：'AnyObject'

Question

我有这个协议：

protocol Container: class where Self: UIViewController {
    var containerView: UIView! { get }
    var currentChild: UIViewController? { get set }
    func remove(child viewController: UIViewController)
    func add(child viewController: UIViewController)
    func replaceCurrentViewController(with newChild: UIViewController)
}

我面临的问题是它显示以下警告

冗余约束 'Self' : 'AnyObject'

这是因为我同时使用了 class 和 where Self: UIViewController，但我两者都需要！原因在于我的协议扩展（见下文），我使用 UIViewController 方法，如果我删除 class，我的扩展会显示一个错误，要求添加 mutating，这它不应该有，因为它只是一个类协议。

extension Container {
    func remove(child viewController: UIViewController) {
        viewController.beginAppearanceTransition(false, animated: true)
        viewController.willMove(toParent: nil)
        viewController.removeFromParent()
        viewController.view.removeFromSuperview()
        viewController.endAppearanceTransition()
        currentChild = nil
    }

    func add(child viewController: UIViewController) {
        viewController.beginAppearanceTransition(true, animated: true)
        addChild(viewController)
        viewController.didMove(toParent: self)
        containerView.addSubview(viewController.view)
        viewController.view.frame = containerView.frame
        viewController.endAppearanceTransition()
        currentChild = viewController
    }

    func replaceCurrentViewController(with newChild: UIViewController) {
        if viewIfLoaded != nil, let currentChild = currentChild {
            if let parent = currentChild.parent, parent == self {
                remove(child: currentChild)
            }
            add(child: newChild)
        }
    }
}

那么，有没有更好的解决方案？我可以删除警告吗？

Answer 1

在swift 4中你可以使用

protocol Container where Self: UIViewController {
    var containerView: UIView! { get }
    var currentChild: UIViewController? { get set }
    func remove(child viewController: UIViewController)
    func add(child viewController: UIViewController)
    func replaceCurrentViewController(with newChild: UIViewController)
}

在 swift 5 中你可以使用

protocol Container: UIViewController {
    var containerView: UIView! { get }
    var currentChild: UIViewController? { get set }
    func remove(child viewController: UIViewController)
    func add(child viewController: UIViewController)
    func replaceCurrentViewController(with newChild: UIViewController)
}

Answer 2

您实际上应该将where 子句放在extension 中，并将具有默认实现的UIViewController 特定方法放在extension 中，这样只有UIViewController 才能访问这些方法。

protocol Container: class {
    var containerView: UIView! { get }
    var currentChild: UIViewController? { get set }
}

extension Container where Self: UIViewController {
    func remove(child viewController: UIViewController) {
        viewController.beginAppearanceTransition(false, animated: true)
        viewController.willMove(toParent: nil)
        viewController.removeFromParent()
        viewController.view.removeFromSuperview()
        viewController.endAppearanceTransition()
        currentChild = nil
    }

    func add(child viewController: UIViewController) {
        viewController.beginAppearanceTransition(true, animated: true)
        addChild(viewController)
        viewController.didMove(toParent: self)
        containerView.addSubview(viewController.view)
        viewController.view.frame = containerView.frame
        viewController.endAppearanceTransition()
        currentChild = viewController
    }

    func replaceCurrentViewController(with newChild: UIViewController) {
        if viewIfLoaded != nil, let currentChild = currentChild {
            if let parent = currentChild.parent, parent == self {
                remove(child: currentChild)
            }
            add(child: newChild)
        }
    }
}