Swift - UIKit - UIColor

UIColor.swift

import UIKit

extension UIColor {
    /// An object that stores color data and sometimes opacity.
    ///
    /// This failable convenience init allows to create an `UIColor` from a hexadecimal `String`. Supported format examples:
    /// - #FFF = UIExtendedSRGBColorSpace 1 1 1 1
    /// - #FFF0 = UIExtendedSRGBColorSpace 1 1 1 0
    /// - #FFFFFF = UIExtendedSRGBColorSpace 1 1 1 1
    /// - #FFFFFF0 = UIExtendedSRGBColorSpace 1 1 1 0
    /// - #FFFFFF00 = UIExtendedSRGBColorSpace 1 1 1 0
    convenience init?(hex: String) {
        if !hex.hasPrefix("#") || ![4, 5, 7, 9].contains(hex.count) {
            return nil
        }

        let start = hex.index(hex.startIndex, offsetBy: 1)
        var color = String(hex[start...])

        if [3, 4].contains(color.count) {
            for i in 0..<color.count * 2 {
                if i % 2 == 0 {
                    continue
                }
                let index = color.index(color.startIndex, offsetBy: i - 1)
                let nextIndex = color.index(after: index)
                let char = color[index]
                color.insert(char, at: nextIndex)
            }
        }

        if color.count == 6 {
            color.append("FF")
        }

        var number: UInt64 = 0
        let scanner = Scanner(string: color)
        if !scanner.scanHexInt64(&number) {
            return nil
        }

        let red, green, blue, alpha: CGFloat
        red = CGFloat((number & 0xff000000) >> 24) / 255
        green = CGFloat((number & 0x00ff0000) >> 16) / 255
        blue = CGFloat((number & 0x0000ff00) >> 8) / 255
        alpha = CGFloat(number & 0x000000ff) / 255
        self.init(red: red, green: green, blue: blue, alpha: alpha)
    }
}