Swift:如何在回调闭包中使用 instanceType

Question

我想将 self 作为 instancetype 传递给这个函数的回调闭包:

extension UIView {
    public func onTap(_ handler: @escaping (_ gesture: UITapGestureRecognizer, _ view: Self) -> Void) -> UITapGestureRecognizer {
        ...
    }
}

let view = UIView.init()
view.onTap { tap, v in
    ...
}

但是我得到一个错误:

Self' is only available in a protocol or as the result of a method in a class; did you mean 'UIView'?

我该怎么做？

Answer 1

当您可以在 Swift 中非常有效地使用协议(protocol)和扩展时，这就是完美的场景(按照书本):

protocol Tappable { }

extension Tappable { // or alternatively: extension Tappable where Self: UIView {
    func onTap(_ handler: @escaping (UITapGestureRecognizer, Self) -> Void) -> UITapGestureRecognizer {
        return UITapGestureRecognizer() // as default to make this snippet sane
    }
}

extension UIView: Tappable { }

---

然后例如:

let button = UIButton.init()
button.onTap { tap, v in
    // v is UIButton...
}

例如:

let label = UILabel.init()
label.onTap { tap, v in
    // v is UILabel...
}

等...

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注意:您可以阅读有关 Extensions 的更多信息或 Protocols在Swift Programming Language Book来自 Apple。