Convert a string representing a CSS hex colour to a UIColor in Swift.

colorFromHexString.swift

/// Get the UIColor corresponding to a CSS hex color code (RGB[A] or RRGGBB[AA])
///
/// - Parameter hex: A hexadecimal representation of the colou
/// - Returns: The UIColor represented by the hexidecimal color code, or UIColor.clear if parsing failed
func colorFromHexString (hex:String) -> UIColor {

    // Remove padding, leading hash symbol etc.
    let hex = hex.trimmingCharacters(in: NSCharacterSet.alphanumerics.inverted)

    // Get numeric representation
    var int = UInt32()
    guard Scanner(string: hex).scanHexInt32(&int) else {
        return UIColor.clear
    }

    // Split into components
    let r, g, b, a: UInt32
    switch hex.characters.count {
    case 3: // RGB
        (r, g, b, a) = ((int >> 8) * 17, (int >> 4 & 0xf) * 17, (int & 0xf) * 17, 255)
    case 4: // RGBA
        (r, g, b, a) = ((int >> 12) * 17, (int >> 8 & 0xf) * 17, (int >> 4 & 0xf) * 17, (int & 0xf) * 17)
    case 6: // RRGGBB
        (r, g, b, a) = (int >> 16, int >> 8 & 0xff, int & 0xff, 255)
    case 8: // RRGGBBAA
        (r, g, b, a) = (int >> 24, int >> 16 & 0xff, int >> 8 & 0xff, int & 0xff)
    default:
        return UIColor.clear
    }

    return UIColor(red: CGFloat(r) / 255, green: CGFloat(g) / 255, blue: CGFloat(b) / 255, alpha: CGFloat(a) / 255)
}