如何使用Swift 4/5扩展多个类

Question

我正在尝试扩展多个类，即UIButton和UITextField。 它们都具有相同的功能，在我调用该功能时可以摆动。 我试图不重复我的代码不止一次。 我一直在尝试使用protocal，以便可以扩展并编写所需的函数，然后在我的类中对其进行扩展，但是问题出在我的函数中，我必须调用self，但是由于self可以仅在UITextField和UIButton上调用。

这是我的代码

import UIKit

extension UIButton {

    func wiggle() {
        let position = "position"
        let wiggleAnimation = CABasicAnimation(keyPath: position)
        wiggleAnimation.duration = 0.05
        wiggleAnimation.repeatCount = 5
        wiggleAnimation.autoreverses = true
        wiggleAnimation.fromValue = CGPoint(x: self.center.x - 4.0, y: self.center.y)
        wiggleAnimation.toValue = CGPoint(x: self.center.x + 4.0, y: self.center.y)
        layer.add(wiggleAnimation, forKey: position)
    }

}

extension UITextField {

    func wiggle() {
        let position = "position"
        let wiggleAnimation = CABasicAnimation(keyPath: position)
        wiggleAnimation.duration = 0.05
        wiggleAnimation.repeatCount = 5
        wiggleAnimation.autoreverses = true
        wiggleAnimation.fromValue = CGPoint(x: self.center.x - 4.0, y: self.center.y)
        wiggleAnimation.toValue = CGPoint(x: self.center.x + 4.0, y: self.center.y)
        layer.add(wiggleAnimation, forKey: position)
    }

}

这是我尝试尝试的操作，但由于我打电话给自己而出现错误。

protocol Animations {
    func wiggle()
}

extension Animations {
    func wiggle() {
        let position = "position"
        let wiggleAnimation = CABasicAnimation(keyPath: position)
        wiggleAnimation.duration = 0.05
        wiggleAnimation.repeatCount = 5
        wiggleAnimation.autoreverses = true
        wiggleAnimation.fromValue = CGPoint(x: self.center.x - 4.0, y: self.center.y)
        wiggleAnimation.toValue = CGPoint(x: self.center.x + 4.0, y: self.center.y)
        layer.add(wiggleAnimation, forKey: position)
    }
}

extension UIButton: Animations {}

extension UITextField: Animations {}

我收到的错误是'Self'类型的值没有成员'center''Self'类型的值没有成员'center'使用了未解析的标识符'layer'

Answer 1

仅UIView具有center属性。 对于Swift 5+，您的协议声明应如下所示：

protocol Animations: UIView {
    func wiggle()
}

注意只有UIViews才能符合此协议。

对于Swift 4.x，您必须像这样使用它：

protocol Animations {
    func wiggle()
}

extension Animations where Self: UIView {
   func wiggle() {
        let position = "position"
        let wiggleAnimation = CABasicAnimation(keyPath: position)
        wiggleAnimation.duration = 0.05
        wiggleAnimation.repeatCount = 5
        wiggleAnimation.autoreverses = true
        wiggleAnimation.fromValue = CGPoint(x: self.center.x - 4.0, y: self.center.y)
        wiggleAnimation.toValue = CGPoint(x: self.center.x + 4.0, y: self.center.y)
        layer.add(wiggleAnimation, forKey: position)
    }
}

Answer 2

前面给出的答案实际上无法使用Swift 4.x进行编译，因为协议无法直接从Swift 5之前的类继承。

在Swift 4.x中编写此代码的正确方法包括仅在符合类型从UIView继承时才为wiggle()函数提供默认实现。 正确的写法是：

protocol Animations {
    func wiggle()
}
extension Animations where Self: UIView {
   func wiggle() {
        let position = "position"
        let wiggleAnimation = CABasicAnimation(keyPath: position)
        wiggleAnimation.duration = 0.05
        wiggleAnimation.repeatCount = 5
        wiggleAnimation.autoreverses = true
        wiggleAnimation.fromValue = CGPoint(x: self.center.x - 4.0, y: self.center.y)
        wiggleAnimation.toValue = CGPoint(x: self.center.x + 4.0, y: self.center.y)
        layer.add(wiggleAnimation, forKey: position)
    }
}