如何在现有 UIKit 类(如 UIColor)的扩展中添加初始值设定项?

问题描述

Swift 文档说可以在扩展中添加初始化器，文档中的示例是关于向 struct 添加初始化器.Xcode 在我的便利初始化程序中无法识别 UIColor 的指定初始化程序:

The Swift documentation says that adding initializers in an extension is possible, and the example in the document is about adding an initializer to a struct. Xcode doesn't recognize UIColor's designated initializer in my convenience initializer:

extension UIColor {
  convenience init(rawValue red: CGFloat, green g: CGFloat, blue b: CGFloat, alpha a: CGFloat) {

    // Can not find out the designated initializer here
    self.init()

  }
}

有什么解决办法吗?

推荐答案

你不能这样做，你必须选择不同的参数名称来创建你自己的初始化器/你也可以让 then generic 接受任何 BinaryInteger 或BinaryFloatingPoint 类型:

You can't do it like this, you have to chose different parameter names to create your own initializers/ You can also make then generic to accept any BinaryInteger or BinaryFloatingPoint types:

extension UIColor {
    convenience init<T: BinaryInteger>(r: T, g: T, b: T, a: T = 255) {
        self.init(red: .init(r)/255, green: .init(g)/255, blue: .init(b)/255, alpha: .init(a)/255)
    }
    convenience init<T: BinaryFloatingPoint>(r: T, g: T, b: T, a: T = 1.0) {
        self.init(red: .init(r), green: .init(g), blue: .init(b), alpha: .init(a))
    }
}

---

let green1 = UIColor(r: 0, g: 255, b: 0, a: 255)  // r 0,0 g 1,0 b 0,0 a 1,0
let green2 = UIColor(r: 0, g: 1.0, b: 0, a: 1.0)  // r 0,0 g 1,0 b 0,0 a 1,0

let red1 = UIColor(r: 255, g: 0, b: 0)  // r 1,0 g 0,0 b 0,0 a 1,0
let red2 = UIColor(r: 1.0, g: 0, b: 0)  // r 1,0 g 0,0 b 0,0 a 1,0

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