How can I make a Swift enum with UIColor value?

Question

I\'m making a drawing app and I would like to refer to my colors through use of an enum. For example, it would be cleaner and more convenient to use Colors.RedColor

Answer 1

How can I make a Swift enum with UIColor value?

This is how you would literally make an enum with a UIColor value:

import UIKit

final class Color: UIColor, RawRepresentable, ExpressibleByStringLiteral
{
    // MARK:- ExpressibleByStringLiteral

    typealias StringLiteralType = String

    convenience init(stringLiteral: String) {
        guard let (a,r,g,b) = Color.argb(hexColor: stringLiteral) else {
            assertionFailure("Invalid string")
            self.init(red: 0, green: 0, blue: 0, alpha: 0)
            return
        }
        self.init(red: r, green: g, blue: b, alpha: a)
    }

    // MARK:- RawRepresentable

    public typealias RawValue = String

    convenience init?(rawValue: RawValue) {
        guard let (a,r,g,b) = Color.argb(hexColor: rawValue) else { return nil }
        self.init(red: r, green: g, blue: b, alpha: a)
    }

    var rawValue: RawValue {
        return hexString()
    }

    // MARK:- Private

    /// Return color components in range [0,1] for hexadecimal color strings.
    /// - hexColor: case-insensitive string with format RGB, RRGGBB, or AARRGGBB.
    private static func argb(hexColor: String) -> (CGFloat,CGFloat,CGFloat,CGFloat)?
    {
        let hexAlphabet = "0123456789abcdefABCDEF"
        let hex = hexColor.trimmingCharacters(in: CharacterSet(charactersIn: hexAlphabet).inverted)
        var int = UInt32()
        Scanner(string: hex).scanHexInt32(&int)
        let a, r, g, b: UInt32
        switch hex.count {
        case 3: (a, r, g, b) = (255, (int >> 8) * 17, (int >> 4 & 0xF) * 17, (int & 0xF) * 17) // RGB
        case 6: (a, r, g, b) = (255, int >> 16, int >> 8 & 0xFF, int & 0xFF) // RRGGBB
        case 8: (a, r, g, b) = (int >> 24, int >> 16 & 0xFF, int >> 8 & 0xFF, int & 0xFF) // AARRGGBB
        default: return nil
        }
        return (CGFloat(a)/255, CGFloat(r)/255, CGFloat(g)/255, CGFloat(b)/255)
    }

    private func hexString() -> String {
        var red:   CGFloat = 0
        var green: CGFloat = 0
        var blue:  CGFloat = 0
        var alpha: CGFloat = 0
        if self.getRed(&red, green: &green, blue: &blue, alpha: &alpha) {
            return String(format: "#%02X%02X%02X%02X", UInt8(red * 255), UInt8(green * 255), UInt8(blue * 255), UInt8(alpha * 255))
        }
        assertionFailure("Invalid colour space.")
        return "#F00"
    }
}

enum Colors: Color {
    case red = "#F00"
//    case blue = "#F00" // Raw value for enum case is not unique
}

let color3 = Color(rawValue: "#000") // RGB
let color6 = Color(rawValue: "#123456") // RRGGBB
let color8 = Color(rawValue: "#12345678") // AARRGGBB
print(Colors(rawValue:"#F00") as Any) // red
print(Colors(rawValue:"#FF0000") as Any) // red
print(Colors(rawValue:"#FFFF0000") as Any) // red
print(Colors(rawValue:"#ABC") as Any) // nil because it’s not a member of the enumeration
// print(Colors(rawValue:"#XYZ") as Any) // assertion on debug, black on release
print(Colors.red) // red
print(Colors.red.rawValue) // UIExtendedSRGBColorSpace 1 0 0 1

With help from

• benhurott/UIColorExtension.md
• Swift 3 UIColor utilities for random color and color from hex code
• Raw type 'Bool' is not expressible by any literal