[Swift]扩展UIColor：实现十六进制颜色字符串与UIColor之间的相互转换

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对【UIColor】进行扩展

import UIKit
 
extension UIColor {
     
    // Hex String -> UIColor
    convenience init(hexString: String) {
        let hexString = hexString.trimmingCharacters(in: .whitespacesAndNewlines)
        let scanner = Scanner(string: hexString)
         
        if hexString.hasPrefix("#") {
            scanner.scanLocation = 1
        }
         
        var color: UInt32 = 0
        scanner.scanHexInt32(&color)
         
        let mask = 0x000000FF
        let r = Int(color >> 16) & mask
        let g = Int(color >> 8) & mask
        let b = Int(color) & mask
         
        let red   = CGFloat(r) / 255.0
        let green = CGFloat(g) / 255.0
        let blue  = CGFloat(b) / 255.0
         
        self.init(red: red, green: green, blue: blue, alpha: 1)
    }
     
    // UIColor -> Hex String
    var hexString: String? {
        var red: CGFloat = 0
        var green: CGFloat = 0
        var blue: CGFloat = 0
        var alpha: CGFloat = 0
         
        let multiplier = CGFloat(255.999999)
         
        guard self.getRed(&red, green: &green, blue: &blue, alpha: &alpha) else {
            return nil
        }
         
        if alpha == 1.0 {
            return String(
                format: "#%02lX%02lX%02lX",
                Int(red * multiplier),
                Int(green * multiplier),
                Int(blue * multiplier)
            )
        }
        else {
            return String(
                format: "#%02lX%02lX%02lX%02lX",
                Int(red * multiplier),
                Int(green * multiplier),
                Int(blue * multiplier),
                Int(alpha * multiplier)
            )
        }
    }
}

测试示例：

// 16进制颜色 -> UIColor
let color = UIColor(hexString: "#A1A1A1")
print("UIColor：", color)
         
// UIColor -> 16进制颜色
let hexString = color.hexString
print("16进制颜色值：", hexString ?? "")

测试结果：

UIColor： UIExtendedSRGBColorSpace 0.631373 0.631373 0.631373 1
16进制颜色值： #A1A1A1