hex string to UIColor

Extension+UIColor.swift

public extension UIColor {
    /// "#RRGGBB", "#RRGGBBAA"
    convenience init?(hex: String) {
        var hexString = hex.trimmingCharacters(in: .whitespacesAndNewlines).uppercased()
        
        if hexString.hasPrefix("#") {
            hexString.remove(at: hexString.startIndex)
        }
        
        guard hexString.count == 6 || hexString.count == 8 else {
            return nil
        }
        
        let scanner = Scanner(string: hexString)
        
        var rgbValue: UInt64 = 0
        guard scanner.scanHexInt64(&rgbValue) else {
            return nil
        }
        
        let red, green, blue, alpha: CGFloat
        if hexString.count == 6 {
            red = CGFloat((rgbValue & 0xFF0000) >> 16) / 255.0
            green = CGFloat((rgbValue & 0x00FF00) >> 8) / 255.0
            blue = CGFloat(rgbValue & 0x0000FF) / 255.0
            alpha = 1.0
        } else {
            red = CGFloat((rgbValue & 0xFF000000) >> 24) / 255.0
            green = CGFloat((rgbValue & 0x00FF0000) >> 16) / 255.0
            blue = CGFloat((rgbValue & 0x0000FF00) >> 8) / 255.0
            alpha = CGFloat(rgbValue & 0x000000FF) / 255.0
        }
        
        self.init(red: red, green: green, blue: blue, alpha: alpha)
    }
    
}