UIColor 扩展方便初始化不起作用

Question

convenience init(red:Int,green:Int,blue:Int,alpha:CGFloat) {
    var red:   CGFloat = CGFloat(red)/255.0
    var green: CGFloat = CGFloat(green)/255.0
    var blue:  CGFloat = CGFloat(blue)/255.0
    self.init(red:red, green:green, blue:blue, alpha:alpha)
}

我编写了上面的代码，以提供更方便的方式来声明我的自定义 uicolor。但不知何故，它通过调用自己直到堆栈溢出来崩溃我的应用程序。这是怎么回事？

另外，我刚刚意识到我没有显式调用这个 init 函数。而是在发生此错误时调用UIColor.whiteColor()。当然，如果我显式调用此函数，仍然会发生错误！

Answer 1

我认为这样做没有任何

不便：

let myCustomColorHSBa = UIColor(hue: 120/360, saturation: 0.25 , brightness: 1.0 , alpha: 1)
let myCustomColorRGBa = UIColor(red: 191/255, green: 1, blue: 191/255, alpha: 1)

但是，如果您确实需要一个，则可以执行以下操作：

extension UIColor {
    convenience init(red: Int = 0, green: Int = 0, blue: Int = 0, opacity: Int = 255) {
        precondition(0...255 ~= red   &&
                     0...255 ~= green &&
                     0...255 ~= blue  &&
                     0...255 ~= opacity, "input range is out of range 0...255")
        self.init(red: CGFloat(red)/255, green: CGFloat(green)/255, blue: CGFloat(blue)/255, alpha: CGFloat(opacity)/255)
    }
}

---

UIColor(red: 255)               // r 1.0 g 0.0 b 0.0 a 1.0  (Red)
UIColor(red: 255, green: 255)   // r 1.0 g 1.0 b 0.0 a 1.0  (Yellow)
UIColor(red: 255, blue: 255)    // r 1.0 g 0.0 b 1.0 a 1.0  (Magenta)
UIColor(green: 255)             // r 0.0 g 1.0 b 0.0 a 1.0  (Green)
UIColor(green: 255, blue: 255)  // r 0.0 g 1.0 b 1.0 a 1.0  (Cyan)
UIColor(blue: 255)              // r 0.0 g 0.0 b 1.0 a 1.0  (Blue)
UIColor(red: 255, green: 192, blue: 203)  // r 1.0 g 0.753 b 0.796 a 1.0 (Pink)
UIColor(red: 255, green: 215)   // r 1.0 g 0.843 b 0.0 a 1.0 (Gold)

Answer 2

另一种方法是这样做（swift 3）

extension UIColor {
    convenience init(r: CGFloat, g: CGFloat, b: CGFloat, a:CGFloat) {
        self.init(red: r/255, green: g/255, blue: b/255, alpha: a/255)
    }  
}
let myColor = UIColor(r:255, g:255, b:255, a:255)