Swift 4: Convert CSS color names and RGB hex values to UIColor. UIColor from hex 3, 4, 6, and 8 characters in length with or without # prefix. UIColor to hex. UIColor extension that creates immutable UIColor instances from hexadecimal and CSS color name strings (e.g. ff0, #f00, ff0000, ff0000ff, Pink, aZure, CLEAR, nil). Conversely, you can obta…

UIColor.swift

//
//  UIColor.swift
//  previously Color+HexAndCSSColorNames.swift
//
//  Created by Norman Basham on 12/8/15.
//  Copyright ©2018 Black Labs. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

import UIKit

public extension UIColor {

    /**
     Creates an immuatble UIColor instance specified by a hex string, CSS color name, or nil.

     - parameter hexString: A case insensitive String? representing a hex or CSS value e.g.

     - **"abc"**
     - **"abc7"**
     - **"#abc7"**
     - **"00FFFF"**
     - **"#00FFFF"**
     - **"00FFFF77"**
     - **"Orange", "Azure", "Tomato"** Modern browsers support 140 color names (<http://www.w3schools.com/cssref/css_colornames.asp>)
     - **"Clear"** [UIColor clearColor]
     - **"Transparent"** [UIColor clearColor]
     - **nil** [UIColor clearColor]
     - **empty string** [UIColor clearColor]
     */
    public convenience init(hex: String?) {
        let normalizedHexString: String = UIColor.normalize(hex)
        var c: CUnsignedInt = 0
        Scanner(string: normalizedHexString).scanHexInt32(&c)
        self.init(red:UIColorMasks.redValue(c), green:UIColorMasks.greenValue(c), blue:UIColorMasks.blueValue(c), alpha:UIColorMasks.alphaValue(c))
    }

    /**
     Returns a hex equivalent of this UIColor.

     - Parameter includeAlpha:   Optional parameter to include the alpha hex.

     color.hexDescription() -> "ff0000"

     color.hexDescription(true) -> "ff0000aa"

     - Returns: A new string with `String` with the color's hexidecimal value.
     */
    public func hexDescription(_ includeAlpha: Bool = false) -> String {
        guard self.cgColor.numberOfComponents == 4 else {
            return "Color not RGB."
        }
        let a = self.cgColor.components!.map { Int($0 * CGFloat(255)) }
        let color = String.init(format: "%02x%02x%02x", a[0], a[1], a[2])
        if includeAlpha {
            let alpha = String.init(format: "%02x", a[3])
            return "\(color)\(alpha)"
        }
        return color
    }

    fileprivate enum UIColorMasks: CUnsignedInt {
        case redMask    = 0xff000000
        case greenMask  = 0x00ff0000
        case blueMask   = 0x0000ff00
        case alphaMask  = 0x000000ff

        static func redValue(_ value: CUnsignedInt) -> CGFloat {
            return CGFloat((value & redMask.rawValue) >> 24) / 255.0
        }

        static func greenValue(_ value: CUnsignedInt) -> CGFloat {
            return CGFloat((value & greenMask.rawValue) >> 16) / 255.0
        }

        static func blueValue(_ value: CUnsignedInt) -> CGFloat {
            return CGFloat((value & blueMask.rawValue) >> 8) / 255.0
        }

        static func alphaValue(_ value: CUnsignedInt) -> CGFloat {
            return CGFloat(value & alphaMask.rawValue) / 255.0
        }
    }

    fileprivate static func normalize(_ hex: String?) -> String {
        guard var hexString = hex else {
            return "00000000"
        }
        if let cssColor = cssToHexDictionairy[hexString.uppercased()] {
            return cssColor.count == 8 ? cssColor : cssColor + "ff"
        }
        if hexString.hasPrefix("#") {
            hexString = String(hexString.dropFirst())
        }
        if hexString.count == 3 || hexString.count == 4 {
            hexString = hexString.map { "\($0)\($0)" } .joined()
        }
        let hasAlpha = hexString.count > 7
        if !hasAlpha {
            hexString += "ff"
        }
        return hexString
    }

    /**
     All modern browsers support the following 140 color names (see http://www.w3schools.com/cssref/css_colornames.asp)
     */
    fileprivate static func hexFromCssName(_ cssName: String) -> String {
        let key = cssName.uppercased()
        if let hex = cssToHexDictionairy[key] {
            return hex
        }
        return cssName
    }

    fileprivate static let cssToHexDictionairy: [String: String] = [
        "CLEAR": "00000000",
        "TRANSPARENT": "00000000",
        "": "00000000",
        "ALICEBLUE": "F0F8FF",
        "ANTIQUEWHITE": "FAEBD7",
        "AQUA": "00FFFF",
        "AQUAMARINE": "7FFFD4",
        "AZURE": "F0FFFF",
        "BEIGE": "F5F5DC",
        "BISQUE": "FFE4C4",
        "BLACK": "000000",
        "BLANCHEDALMOND": "FFEBCD",
        "BLUE": "0000FF",
        "BLUEVIOLET": "8A2BE2",
        "BROWN": "A52A2A",
        "BURLYWOOD": "DEB887",
        "CADETBLUE": "5F9EA0",
        "CHARTREUSE": "7FFF00",
        "CHOCOLATE": "D2691E",
        "CORAL": "FF7F50",
        "CORNFLOWERBLUE": "6495ED",
        "CORNSILK": "FFF8DC",
        "CRIMSON": "DC143C",
        "CYAN": "00FFFF",
        "DARKBLUE": "00008B",
        "DARKCYAN": "008B8B",
        "DARKGOLDENROD": "B8860B",
        "DARKGRAY": "A9A9A9",
        "DARKGREY": "A9A9A9",
        "DARKGREEN": "006400",
        "DARKKHAKI": "BDB76B",
        "DARKMAGENTA": "8B008B",
        "DARKOLIVEGREEN": "556B2F",
        "DARKORANGE": "FF8C00",
        "DARKORCHID": "9932CC",
        "DARKRED": "8B0000",
        "DARKSALMON": "E9967A",
        "DARKSEAGREEN": "8FBC8F",
        "DARKSLATEBLUE": "483D8B",
        "DARKSLATEGRAY": "2F4F4F",
        "DARKSLATEGREY": "2F4F4F",
        "DARKTURQUOISE": "00CED1",
        "DARKVIOLET": "9400D3",
        "DEEPPINK": "FF1493",
        "DEEPSKYBLUE": "00BFFF",
        "DIMGRAY": "696969",
        "DIMGREY": "696969",
        "DODGERBLUE": "1E90FF",
        "FIREBRICK": "B22222",
        "FLORALWHITE": "FFFAF0",
        "FORESTGREEN": "228B22",
        "FUCHSIA": "FF00FF",
        "GAINSBORO": "DCDCDC",
        "GHOSTWHITE": "F8F8FF",
        "GOLD": "FFD700",
        "GOLDENROD": "DAA520",
        "GRAY": "808080",
        "GREY": "808080",
        "GREEN": "008000",
        "GREENYELLOW": "ADFF2F",
        "HONEYDEW": "F0FFF0",
        "HOTPINK": "FF69B4",
        "INDIANRED": "CD5C5C",
        "INDIGO": "4B0082",
        "IVORY": "FFFFF0",
        "KHAKI": "F0E68C",
        "LAVENDER": "E6E6FA",
        "LAVENDERBLUSH": "FFF0F5",
        "LAWNGREEN": "7CFC00",
        "LEMONCHIFFON": "FFFACD",
        "LIGHTBLUE": "ADD8E6",
        "LIGHTCORAL": "F08080",
        "LIGHTCYAN": "E0FFFF",
        "LIGHTGOLDENRODYELLOW": "FAFAD2",
        "LIGHTGRAY": "D3D3D3",
        "LIGHTGREY": "D3D3D3",
        "LIGHTGREEN": "90EE90",
        "LIGHTPINK": "FFB6C1",
        "LIGHTSALMON": "FFA07A",
        "LIGHTSEAGREEN": "20B2AA",
        "LIGHTSKYBLUE": "87CEFA",
        "LIGHTSLATEGRAY": "778899",
        "LIGHTSLATEGREY": "778899",
        "LIGHTSTEELBLUE": "B0C4DE",
        "LIGHTYELLOW": "FFFFE0",
        "LIME": "00FF00",
        "LIMEGREEN": "32CD32",
        "LINEN": "FAF0E6",
        "MAGENTA": "FF00FF",
        "MAROON": "800000",
        "MEDIUMAQUAMARINE": "66CDAA",
        "MEDIUMBLUE": "0000CD",
        "MEDIUMORCHID": "BA55D3",
        "MEDIUMPURPLE": "9370DB",
        "MEDIUMSEAGREEN": "3CB371",
        "MEDIUMSLATEBLUE": "7B68EE",
        "MEDIUMSPRINGGREEN": "00FA9A",
        "MEDIUMTURQUOISE": "48D1CC",
        "MEDIUMVIOLETRED": "C71585",
        "MIDNIGHTBLUE": "191970",
        "MINTCREAM": "F5FFFA",
        "MISTYROSE": "FFE4E1",
        "MOCCASIN": "FFE4B5",
        "NAVAJOWHITE": "FFDEAD",
        "NAVY": "000080",
        "OLDLACE": "FDF5E6",
        "OLIVE": "808000",
        "OLIVEDRAB": "6B8E23",
        "ORANGE": "FFA500",
        "ORANGERED": "FF4500",
        "ORCHID": "DA70D6",
        "PALEGOLDENROD": "EEE8AA",
        "PALEGREEN": "98FB98",
        "PALETURQUOISE": "AFEEEE",
        "PALEVIOLETRED": "DB7093",
        "PAPAYAWHIP": "FFEFD5",
        "PEACHPUFF": "FFDAB9",
        "PERU": "CD853F",
        "PINK": "FFC0CB",
        "PLUM": "DDA0DD",
        "POWDERBLUE": "B0E0E6",
        "PURPLE": "800080",
        "RED": "FF0000",
        "ROSYBROWN": "BC8F8F",
        "ROYALBLUE": "4169E1",
        "SADDLEBROWN": "8B4513",
        "SALMON": "FA8072",
        "SANDYBROWN": "F4A460",
        "SEAGREEN": "2E8B57",
        "SEASHELL": "FFF5EE",
        "SIENNA": "A0522D",
        "SILVER": "C0C0C0",
        "SKYBLUE": "87CEEB",
        "SLATEBLUE": "6A5ACD",
        "SLATEGRAY": "708090",
        "SLATEGREY": "708090",
        "SNOW": "FFFAFA",
        "SPRINGGREEN": "00FF7F",
        "STEELBLUE": "4682B4",
        "TAN": "D2B48C",
        "TEAL": "008080",
        "THISTLE": "D8BFD8",
        "TOMATO": "FF6347",
        "TURQUOISE": "40E0D0",
        "VIOLET": "EE82EE",
        "WHEAT": "F5DEB3",
        "WHITE": "FFFFFF",
        "WHITESMOKE": "F5F5F5",
        "YELLOW": "FFFF00",
        "YELLOWGREEN": "9ACD32"
    ]
}

So cool! Save me an hour!! 👍

I think it can be enhanced with:

1. define a typealias for NSColor and UIColor so it can support both macOS and iOS.
2. support specifying color space (or just use NSColor(srgbRed:green:blue:alpha:)) to achieve consistent visual effect.
3. use Scanner.scanHexInt64(:) and UInt64 to avoid using deprecated function.
4. wrap this cool snippet with SPM, and add unit tests for it.
5. remove redundant public modifiers.
6. add input validation, or adding something like strict mode to check the input
7. fix typo: cssToHexDictionairy
8. consider change init(hex:) to init(css:) since it does handle css color, not only hex string

It takes me an extra hour to rewrite it... 😂 anyway thanks

@gongzhang I really appreciate the constructive, useful, and clear suggestions. SPM can be found at BlackLabsColor. Thank you!

Thank!

😄 Here are two suggestions for improvements to hexDescription:

public func hexDescription(_ includeAlpha: Bool = false) -> String? {
    var cgColor = self.cgColor

    // 🌟 1. needs sRGB color space.
    // otherwise this method will fail on UIColor.black or .white since they are in gray scale color space.
    if cgColor.colorSpace?.name != CGColorSpace.sRGB {
        guard let srgb = CGColorSpace(name: CGColorSpace.sRGB) else { return nil }
        guard let srgbColor = cgColor.converted(to: srgb,
                                                intent: CGColorRenderingIntent.defaultIntent,
                                                options: nil) else {
            return nil
        }
        
        cgColor = srgbColor
    }

    guard cgColor.numberOfComponents == 4 else {
        return nil
    }
    
    // 🌟 2. round() before cast CGFloat to Int to get accurate color
    let a = self.cgColor.components!.map { Int(round($0 * CGFloat(255))) }
    ...
}

Good solution, works in my code. Thanks!