ToHexString.swift

func toHexString1(_ color:UIColor) -> String? {
    guard let components = color.cgColor.components else { return nil }
    return toHexString(components)
}

func toHexString2(_ color:UIColor) -> String? {
    var r: CGFloat = 0
    var g: CGFloat = 0
    var b: CGFloat = 0
    var a: CGFloat = 0
    guard color.getRed(&r, green: &g, blue: &b, alpha: &a) else { return nil }
    return toHexString([r, g, b, a])
}

func toHexString3(_ color:UIColor) -> String? {
    let ciColor = CIColor(cgColor: color.cgColor)
    return toHexString([ciColor.red, ciColor.green, ciColor.blue, ciColor.alpha])
}

func toHexString(_ components:[CGFloat]) -> String? {
    if components.count < 3 { return nil }
    let r = Float(components[0])
    let g = Float(components[1])
    let b = Float(components[2])
    let a = components.count >= 4 ? Float(components[3]) : 1.0
    if a != 1 {
        return String(format: "#%02lX%02lX%02lX%02lX", lroundf(r * 255), lroundf(g * 255), lroundf(b * 255), lroundf(a * 255))
    } else {
        return String(format: "#%02lX%02lX%02lX", lroundf(r * 255), lroundf(g * 255), lroundf(b * 255))
    }
}