如何在 Swift 中定义使用 class 类型作为参数的 function？

Question

I simply try to do the following:

func popTo(classType: AnyClass, from context: UINavigationController?) {
    let controller = context?.viewControllers.first { $0 is classType }
    context?.popToViewController(controller, animated: true)
}

I need to use it like this:

popTo(SettingsViewController.self, from: navigationController)

Answer 1

As far as the compiler is concerned, classType isn't a type like String or Int . It's just the name of a parameter (which stores a type). But the is operator expects a type (that can be resolved at compile time) on its RHS.

We need a type that is known at compile time. We can pass such a type parameter with generics:

func popTo<T>(classType: T.Type, from context: UINavigationController?) {
    if let controller = context?.viewControllers.first(where: { $0 is T }) {
        context?.popToViewController(controller, animated: true)
    }
}

You can also add the constraint T: AnyObject to more closely reflect the AnyClass (= AnyObject.Type ) in your original code, but you don't particularly have to.

Answer 2

func popTo<T: UIViewController>(classType: T.Type, from context: UINavigationController?) {
    let controller = context?.viewControllers.first { $0 is T }
    context?.popToViewController(controller!, animated: true)
}