创建一个类型为 UIView 的变量，该变量符合 swift 中的协议

Question

Inside a class, I want to add a variable of type UIView, which conforms to the following protocol:

public protocol Shadow: UIView {
    func applyShadow()
}

public extension Shadow {
    func applyShadow() {
        self.layer.cornerRadius = 16
        ...
    }
}

To then be able to do something like this:

private lazy var shadowView: Shadow = UIView()
shadowView.applyShadow()

I want to do this, so I don't have to bring that function applyShadow() to my class and have repeated code.

Answer 1

Then you need to declare as below

public protocol Shadow {
    func applyShadow()
}

public extension Shadow where Self: UIView {
    func applyShadow() {
        self.layer.cornerRadius = 16
    }
}

Answer 2

Basically, there are 2 ways to do this. One is having a protocol Shadow then creating a concrete class to conform to Shadow protocol as below

public protocol Shadowable where Self: UIView {
    func applyShadow()
}

public class Shadow: UIView, Shadowable {
    func applyShadow() {
        self.layer.cornerRadius = 16
    }
}

Or you can create an extension of UIView in Shadow class

class Shadow: UIView {}

extension UIView {
    func applyShadow() {
        self.layer.cornerRadius = 16
    }
}

Answer 3

The comment box is very limited to the character counts. so I create another answer

public protocol Shadow: UIView {
    func applyShadow()
}

public extension Shadow {
    func applyShadow() {
        self.layer.cornerRadius = 16
    }
}

// re-use Shadow protocol 
//this is a concrete class that conforms to Shadow protocol 
class CardWithTitle: UIView, Shadow {}


class Card: UIView {
   private lazy var oneVariable: CardWithTitle = {
        let view = CardWithTitle()
        view.applyShadow()
        return view
    }()
}