ios - 从协议(protocol)扩展调用选择器

Question

我正在构建简单的主题引擎，并且想要一个将 UISwipeGestureRecognizer 添加到 UIViewController 的扩展

这是我的代码:

protocol Themeable {
    func themeDidUpdate(currentTheme: Theme) -> Void
}

extension Themeable where Self: UIViewController {
    func switchCurrentTheme() {
        Theme.switchTheme()
        themeDidUpdate(Theme.currentTheme)
    }

    func addSwitchThemeGestureRecognizer() {
        let gestureRecognizer = UISwipeGestureRecognizer(target: self, action:#selector(Self.switchCurrentTheme))
        gestureRecognizer.direction = .Down
        gestureRecognizer.numberOfTouchesRequired = 2
        self.view.addGestureRecognizer(gestureRecognizer)
    }
}

当然，编译器找不到 #selector(Self.switchCurrentTheme)，因为它没有通过 @objc 指令公开。是否可以将此行为添加到我的扩展中？

更新: Theme 是一个 Swift 枚举，所以我不能在 Themeable 前面添加 @objc > 协议(protocol)

Answer 1

我能想到的最干净、可行的解决方案是使用相关方法在 UIViewController 上定义一个私有(private)扩展。通过将范围限制为 private，可以将对此方法的访问隔离到定义协议(protocol)的源文件中。如下所示:

protocol Themeable {
    func themeDidUpdate(currentTheme: Theme) -> Void
}

fileprivate extension UIViewController {
    @objc func switchCurrentTheme() {
        guard let themeableSelf = self as? Themeable else {
            return
        }

        Theme.switchTheme()
        themeableSelf.themeDidUpdate(Theme.currentTheme)
    }
}

extension Themeable where Self: UIViewController {
    func addSwitchThemeGestureRecognizer() {
        let gestureRecognizer = UISwipeGestureRecognizer(target: self, action:#selector(switchCurrentTheme))
        gestureRecognizer.direction = .Down
        gestureRecognizer.numberOfTouchesRequired = 2
        self.view.addGestureRecognizer(gestureRecognizer)
    }
}