带有按钮和选择器的协议扩展

Question

我有一些协议：

@objc protocol SomeProtocol { }

我扩展了 UIViewController 个实例。在此扩展中，我想创建并添加一个按钮，其选择器也在协议中定义：

extension SomeProtocol where Self: UIViewController {

    func addSomeButton() {
        let someButton = UIButton()
        someButton.addTarget(self, #selector(someButtonPressed), for: .touchUpInside)
        view.addSubview(someButton)
    }

    @objc func someButtonPressed() {
    }

}

但是，我收到错误 @objc can only be used with members of 类、@objc protocols 和类 的具体扩展someButtonPressed.

的定义

有什么方法可以使用协议来实现吗？

提前感谢您的任何建议！

Answer 1

您需要在协议中提供 Selector 要求。这是因为您只能将 @objc 属性应用于 NSObject。标记协议 @objc 的唯一原因是为了可选方法。

@objc protocol SomeProtocol {
    var action: Selector { get }
}

将扩展名更改为：

extension SomeProtocol where Self: UIViewController {
    func addSomeButton() {
        let someButton = UIButton()
        someButton.addTarget(self, action: action, for: .touchUpInside)
        view.addSubview(someButton)
    }
}

现在，这有效：

extension UIViewController: SomeProtocol {
    @objc func buttonPressed(sender: UIButton) {
        print("Button pressed")
    }
    var action: Selector {
        return #selector(buttonPressed(sender:))
    }
}

用法：

let vc: myViewController: MyViewController!
func doSomething() {
  vc.addSomeButton()
}

Answer 2

一种解决方法是向 UIButton 添加一个封闭套管而不是此处显示的目标操作并为方便起见复制在下面。

typealias Closure = () -> ()

///
class ClosureSleeve {
    let closure: Closure
    init(_ closure: @escaping Closure) {
        self.closure = closure
    }
    @objc func invoke () {
        closure()
    }
}

extension UIControl {
    func addAction(for controlEvents: UIControl.Event = .touchUpInside, _ closure: @escaping Closure) {
        let sleeve = ClosureSleeve(closure)
        addTarget(sleeve, action: #selector(ClosureSleeve.invoke), for: controlEvents)
        objc_setAssociatedObject(self, String(format: "[%d]", arc4random()), sleeve, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
    }
}

然后简单地替换：

someButton.addTarget(self, #selector(someButtonPressed), for: .touchUpInside)

与：

someButton.addAction { [weak self] in
        self?.someButtonPressed()
    }

嘿嘿。

带有按钮和选择器的协议扩展

Protocol extension with button and selector

protocols

selector

uibutton

ios

swift