[Swift 开发] iOS 颜色值#ffffff转UIColor

写代码颜色值的时候会用到#ffffff 这样的格式，UIColor不能直接识别，我们要转换一下。

在SwiftTheme中看到了这个功能，在这里分享一下。

public enum UIColorInputError : Error {    case missingHashMarkAsPrefix,    unableToScanHexValue,    mismatchedHexStringLength}extension UIColor {    /**     The shorthand three-digit hexadecimal representation of color.     #RGB defines to the color #RRGGBB.          - parameter hex3: Three-digit hexadecimal value.     - parameter alpha: 0.0 - 1.0. The default is 1.0.     */    public convenience init(hex3: UInt16, alpha: CGFloat = 1) {        let divisor = CGFloat(15)        let red     = CGFloat((hex3 & 0xF00) >> 8) / divisor        let green   = CGFloat((hex3 & 0x0F0) >> 4) / divisor        let blue    = CGFloat( hex3 & 0x00F      ) / divisor        self.init(red: red, green: green, blue: blue, alpha: alpha)    }        /**     The shorthand four-digit hexadecimal representation of color with alpha.     #RGBA defines to the color #RRGGBBAA.          - parameter hex4: Four-digit hexadecimal value.     */    public convenience init(hex4: UInt16) {        let divisor = CGFloat(15)        let red     = CGFloat((hex4 & 0xF000) >> 12) / divisor        let green   = CGFloat((hex4 & 0x0F00) >>  8) / divisor        let blue    = CGFloat((hex4 & 0x00F0) >>  4) / divisor        let alpha   = CGFloat( hex4 & 0x000F       ) / divisor        self.init(red: red, green: green, blue: blue, alpha: alpha)    }        /**     The six-digit hexadecimal representation of color of the form #RRGGBB.          - parameter hex6: Six-digit hexadecimal value.     */    public convenience init(hex6: UInt32, alpha: CGFloat = 1) {        let divisor = CGFloat(255)        let red     = CGFloat((hex6 & 0xFF0000) >> 16) / divisor        let green   = CGFloat((hex6 & 0x00FF00) >>  8) / divisor        let blue    = CGFloat( hex6 & 0x0000FF       ) / divisor        self.init(red: red, green: green, blue: blue, alpha: alpha)    }        /**     The six-digit hexadecimal representation of color with alpha of the form #RRGGBBAA.          - parameter hex8: Eight-digit hexadecimal value.     */    public convenience init(hex8: UInt32) {        let divisor = CGFloat(255)        let red     = CGFloat((hex8 & 0xFF000000) >> 24) / divisor        let green   = CGFloat((hex8 & 0x00FF0000) >> 16) / divisor        let blue    = CGFloat((hex8 & 0x0000FF00) >>  8) / divisor        let alpha   = CGFloat( hex8 & 0x000000FF       ) / divisor        self.init(red: red, green: green, blue: blue, alpha: alpha)    }        /**     The rgba string representation of color with alpha of the form #RRGGBBAA/#RRGGBB, throws error.          - parameter rgba: String value.     */    public convenience init(rgba_throws rgba: String) throws {        guard rgba.hasPrefix("#") else {            throw UIColorInputError.missingHashMarkAsPrefix        }                /*guard let hexString: String = rgba.substring(from: rgba.characters.index(rgba.startIndex, offsetBy: 1)),            var   hexValue:  UInt32 = 0, Scanner(string: hexString).scanHexInt32(&hexValue) else {                throw UIColorInputError.unableToScanHexValue        }*/                let hexString: String = String(rgba[rgba.index(rgba.startIndex, offsetBy: 1)...])        var hexValue:  UInt32 = 0        Scanner(string: hexString).scanHexInt32(&hexValue)                guard hexString.characters.count  == 3            || hexString.characters.count == 4            || hexString.characters.count == 6            || hexString.characters.count == 8 else {                throw UIColorInputError.mismatchedHexStringLength        }                switch (hexString.characters.count) {        case 3:            self.init(hex3: UInt16(hexValue))        case 4:            self.init(hex4: UInt16(hexValue))        case 6:            self.init(hex6: hexValue)        default:            self.init(hex8: hexValue)        }    }        /**     The rgba string representation of color with alpha of the form #RRGGBBAA/#RRGGBB, fails to default color.          - parameter rgba: String value.     */    public convenience init(rgba: String, defaultColor: UIColor = UIColor.clear) {        guard let color = try? UIColor(rgba_throws: rgba) else {            self.init(cgColor: defaultColor.cgColor)            return        }        self.init(cgColor: color.cgColor)    }        /**     Hex string of a UIColor instance.          - parameter rgba: Whether the alpha should be included.     */    public func hexString(_ includeAlpha: Bool) -> String {        var r: CGFloat = 0        var g: CGFloat = 0        var b: CGFloat = 0        var a: CGFloat = 0        self.getRed(&r, green: &g, blue: &b, alpha: &a)                if (includeAlpha) {            return String(format: "#%02X%02X%02X%02X", Int(r * 255), Int(g * 255), Int(b * 255), Int(a * 255))        } else {            return String(format: "#%02X%02X%02X", Int(r * 255), Int(g * 255), Int(b * 255))        }    }        open override var description: String {        return self.hexString(true)    }        open override var debugDescription: String {        return self.hexString(true)    }}