更简短的解释:
您经常希望扩展“目标”...而目标通常是 Any?
。但是您不能在 Any
上有扩展名。怎么做?
考虑一下,
extension UIViewController {
func add(tap v:UIView, _ action:Selector) {
let t = UITapGestureRecognizer(target: self, action: action)
v.addGestureRecognizer(t)
}
}
太好了,你现在可以...
self.tap(redButton, #selector(clickedRedButton))
...在任何 View Controller 中。
但您几乎可以对任何目标执行相同的操作。
因此,要在 UITableViewCell 上使用扩展,您还必须拥有....
extension UIGestureRecognizerDelegate {
func add(tap v:UIView, _ action:Selector) {
let t = UITapGestureRecognizer(target: self, action: action)
v.addGestureRecognizer(t)
}
}
UITapGestureRecognizer 的目标参数实际上是 Any?
但是,你不能这样做......
extension Any {
解决方案是什么?如何制作适用于 Any?
的扩展,例如 UITapGestureRecognizer
的第一个参数?
或者正如 Conner 的评论所暗示的那样,有没有办法:
extension UIViewController or UIView {
而不是复制粘贴两次?
最佳答案
每个结构/类都(被动地)遵守“任何”。 Any 的扩展会将该功能添加到语言和代码中的每个类型。目前这是不可能的,我怀疑它是否会(或应该)。
无论如何,这里有几种方法可以解决这个问题。
我的偏好是添加功能的协议(protocol)扩展:
protocol TapGestureAddable {
func addTapGestureRecognizer(to view: UIView, with action: Selector) -> UITapGestureRecognizer
}
extension TapGestureAddable {
func addTapGestureRecognizer(to view: UIView, with action: Selector) -> UITapGestureRecognizer {
let recognizer = UITapGestureRecognizer(target: self, action: action)
view.addGestureRecognizer(recognizer)
return recognizer
}
}
extension UIViewController: TapGestureAddable { }
extension UIView: TapGestureAddable { }
这迫使您有意识地选择将功能添加到给定的类(IMO 是件好事),而不必复制任何有意义的代码。
可能更好的选择是将此逻辑改为 UIView 的扩展:
extension UIView {
func addTapGestureRecognizer(with responder: Any, for action: Selector) -> UITapGestureRecognizer {
let recognizer = UITapGestureRecognizer(target: responder, action: action)
self.addGestureRecognizer(recognizer)
return recognizer
}
func addTapGestureRecognizer(with action: Selector) -> UITapGestureRecognizer {
let recognizer = UITapGestureRecognizer(target: self, action: action)
self.addGestureRecognizer(recognizer)
return recognizer
}
}
否则,只需创建一个全局函数:
func addTapGestureRecognizer(to view: UIView, with responder: Any, for action: Selector) -> UITapGestureRecognizer {
let recognizer = UITapGestureRecognizer(target: responder, action: action)
view.addGestureRecognizer(recognizer)
return recognizer
}
关于ios - "Any?"类的 Swift3 扩展?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41641619/