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

Based on @Jano's answer I made an improvement by using Int as the literal type:

import UIKit

public final class Colors: UIColor {

}

extension Colors: ExpressibleByIntegerLiteral {
    public typealias IntegerLiteralType = Int

    public convenience init(integerLiteral value: Int) {
        let red = CGFloat((value & 0xFF0000FF) >> 24) / 0xFF
        let green = CGFloat((value & 0x00FF00FF) >> 16) / 0xFF
        let blue = CGFloat((value & 0x0000FFFF) >> 8) / 0xFF
        let alpha = CGFloat(value & 0x00FF00FF) / 0xFF

        self.init(red: red, green: green, blue: blue, alpha: alpha)
    }
}

extension Colors: RawRepresentable {
    public typealias RawValue = Int

    public var rawValue: RawValue {
        return hex
    }

    public convenience init?(rawValue: RawValue) {
        self.init(integerLiteral: rawValue)
    }
}

fileprivate extension UIColor {
    var hex: Int {
        var fRed: CGFloat = 0
        var fGreen: CGFloat = 0
        var fBlue: CGFloat = 0
        var fAlpha: CGFloat = 0
        if self.getRed(&fRed, green: &fGreen, blue: &fBlue, alpha: &fAlpha) {
            let red = Int(fRed * 255.0)
            let green = Int(fGreen * 255.0)
            let blue = Int(fBlue * 255.0)
            let alpha = Int(fAlpha * 255.0)
            let rgb = (alpha << 24) + (red << 16) + (green << 8) + blue
            return rgb
        } else {
            return 0x000000
        }
    }
}

public enum MainPalette: Colors {
    case red = 0xFF0000ff
    case white = 0xFFFFFFFF
}

public enum FeatureXPalette: Colors {
    case blue = 0x024F9Eff
//    case bluish = 0x024F9Eff // <- Can't do
    case red = 0xFF0000ff
}

The advantage is that it doesn't allow duplicate colors (as a true enum) and also I support alpha.

As you can see, you can create multiple enums for different palettes/schemes. In the case you want views to be able to use any palette, you can just add a protocol:

protocol Color {
    var color: UIColor { get }
}

extension MainPalette: Color {
    var color: UIColor {
        return rawValue
    }
}

extension FeatureXPalette: Color {
    var color: UIColor {
        return rawValue
    }
}

so that way you can have a function that takes in the protocol:

func printColorEquality(color1: Color, color2: Color) {
    print(color1.color == color2.color)
}

let red1: Color = MainPalette.red
let red2: Color = FeatureXPalette.red

printColorEquality(color1: red1, color2: red2)

What I also like to do is add static vars for convenience:

extension MainPalette {
    public static var brightRed: UIColor {
        return MainPalette.red.color
    }
}

that gives you a cleaner api:

view.backgroundColor = MainPalette.brightRed

Naming can be improved: you have to choose if you want a nice convenience api or nice naming for your enums.