斯威夫特2.0:

做一个UIColor的扩展。

extension UIColor {
    convenience init(hexString:String) {
        let hexString:NSString = hexString.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet())
        let scanner            = NSScanner(string: hexString as String)
        if (hexString.hasPrefix("#")) {
            scanner.scanLocation = 1
        }

        var color:UInt32 = 0
        scanner.scanHexInt(&color)

        let mask = 0x000000FF
        let r = Int(color >> 16) & mask
        let g = Int(color >> 8) & mask
        let b = Int(color) & mask

        let red   = CGFloat(r) / 255.0
        let green = CGFloat(g) / 255.0
        let blue  = CGFloat(b) / 255.0
        self.init(red:red, green:green, blue:blue, alpha:1)
    }

    func toHexString() -> String {
        var r:CGFloat = 0
        var g:CGFloat = 0
        var b:CGFloat = 0
        var a:CGFloat = 0
        getRed(&r, green: &g, blue: &b, alpha: &a)
        let rgb:Int = (Int)(r*255)<<16 | (Int)(g*255)<<8 | (Int)(b*255)<<0
        return NSString(format:"#%06x", rgb) as String
    }

}

用法:

//Hex to Color
    let countPartColor =  UIColor(hexString: "E43038")

//Color to Hex
let colorHexString =  UIColor(red: 228, green: 48, blue: 56, alpha: 1.0).toHexString()

斯威夫特2.0

下面的代码是在xcode 7.2上测试的

import UIKit
extension UIColor{

    public convenience init?(colorCodeInHex: String, alpha: Float = 1.0){

        var filterColorCode:String =  colorCodeInHex.stringByReplacingOccurrencesOfString("#", withString: "")

        if  filterColorCode.characters.count != 6 {
            self.init(red: 0.0, green: 0.0, blue: 0.0, alpha: CGFloat(alpha))
            return
        }

        filterColorCode = filterColorCode.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet()).uppercaseString

        var range = Range(start: filterColorCode.startIndex.advancedBy(0), end: filterColorCode.startIndex.advancedBy(2))
        let rString = filterColorCode.substringWithRange(range)

        range = Range(start: filterColorCode.startIndex.advancedBy(2), end: filterColorCode.startIndex.advancedBy(4))
        let gString = filterColorCode.substringWithRange(range)


        range = Range(start: filterColorCode.startIndex.advancedBy(4), end: filterColorCode.startIndex.advancedBy(6))
        let bString = filterColorCode.substringWithRange(range)

        var r:CUnsignedInt = 0, g:CUnsignedInt = 0, b:CUnsignedInt = 0;
        NSScanner(string: rString).scanHexInt(&r)
        NSScanner(string: gString).scanHexInt(&g)
        NSScanner(string: bString).scanHexInt(&b)


        self.init(red: CGFloat(r) / 255.0, green: CGFloat(g) / 255.0, blue: CGFloat(b) / 255.0, alpha: CGFloat(alpha))
        return
    }
}

这是UIColor的一个Swift扩展，它采用十六进制字符串:

import UIKit

extension UIColor {

    convenience init(hexString: String) {
        // Trim leading '#' if needed
        var cleanedHexString = hexString
        if hexString.hasPrefix("#") {
//            cleanedHexString = dropFirst(hexString) // Swift 1.2
            cleanedHexString = String(hexString.characters.dropFirst()) // Swift 2
        }

        // String -> UInt32
        var rgbValue: UInt32 = 0
        NSScanner(string: cleanedHexString).scanHexInt(&rgbValue)

        // UInt32 -> R,G,B
        let red = CGFloat((rgbValue >> 16) & 0xff) / 255.0
        let green = CGFloat((rgbValue >> 08) & 0xff) / 255.0
        let blue = CGFloat((rgbValue >> 00) & 0xff) / 255.0

        self.init(red: red, green: green, blue: blue, alpha: 1.0)
    }

}

斯威夫特2.3: 用户界面颜色扩展。我认为这样更简单。

extension UIColor {
    static func colorFromHex(hexString: String, alpha: CGFloat = 1) -> UIColor {
        //checking if hex has 7 characters or not including '#'
        if hexString.characters.count < 7 {
            return UIColor.whiteColor()
        }
        //string by removing hash
        let hexStringWithoutHash = hexString.substringFromIndex(hexString.startIndex.advancedBy(1))

        //I am extracting three parts of hex color Red (first 2 characters), Green (middle 2 characters), Blue (last two characters)
        let eachColor = [
            hexStringWithoutHash.substringWithRange(hexStringWithoutHash.startIndex...hexStringWithoutHash.startIndex.advancedBy(1)),
            hexStringWithoutHash.substringWithRange(hexStringWithoutHash.startIndex.advancedBy(2)...hexStringWithoutHash.startIndex.advancedBy(3)),
            hexStringWithoutHash.substringWithRange(hexStringWithoutHash.startIndex.advancedBy(4)...hexStringWithoutHash.startIndex.advancedBy(5))]

        let hexForEach = eachColor.map {CGFloat(Int($0, radix: 16) ?? 0)} //radix is base of numeric system you want to convert to, Hexadecimal has base 16

        //return the color by making color
        return UIColor(red: hexForEach[0] / 255, green: hexForEach[1] / 255, blue: hexForEach[2] / 255, alpha: alpha)
    }
}

用法:

let color = UIColor.colorFromHex("#25ac09")

extension UIColor {
    public convenience init?(hex: String) {
        let r, g, b, a: CGFloat

        if hex.hasPrefix("#") {
            let start = hex.index(hex.startIndex, offsetBy: 1)
            let hexColor = String(hex[start...])

            if hexColor.count == 8 {
                let scanner = Scanner(string: hexColor)
                var hexNumber: UInt64 = 0

                if scanner.scanHexInt64(&hexNumber) {
                    r = CGFloat((hexNumber & 0xff000000) >> 24) / 255
                    g = CGFloat((hexNumber & 0x00ff0000) >> 16) / 255
                    b = CGFloat((hexNumber & 0x0000ff00) >> 8) / 255
                    a = CGFloat(hexNumber & 0x000000ff) / 255

                    self.init(red: r, green: g, blue: b, alpha: a)
                    return
                }
            }
        }

        return nil
    }
}

用法:

let white = UIColor(hex: "#ffffff")

RGBA版本Swift 3/4

我喜欢卢卡的回答，因为我认为它是最优雅的。

然而，我不希望我的颜色指定在ARGB。我宁愿RGBA +，我也需要在处理字符串的情况下，为每个频道指定1个字符“#FFFA”。

这个版本还增加了错误抛出+剥离'#'字符如果它包含在字符串中。 这是我修改后的Swift表格。

public enum ColourParsingError: Error
{
    
    case invalidInput(String)
}
extension UIColor {
    public convenience init(hexString: String) throws
    {
        let hexString = hexString.replacingOccurrences(of: "#", with: "")
        let hex = hexString.trimmingCharacters(in:NSCharacterSet.alphanumerics.inverted)
        var int = UInt32()
        Scanner(string: hex).scanHexInt32(&int)
        let a, r, g, b: UInt32
        switch hex.count 
        {
        case 3: // RGB (12-bit)
            (r, g, b,a) = ((int >> 8) * 17, (int >> 4 & 0xF) * 17, (int & 0xF) * 17,255)
        //iCSS specification in the form of #F0FA
        case 4: // RGB (24-bit)
            (r, g, b,a) = ((int >> 12) * 17, (int >> 8 & 0xF) * 17, (int >> 4 & 0xF) * 17, (int & 0xF) * 17)
        case 6: // RGB (24-bit)
            (r, g, b, a) = (int >> 16, int >> 8 & 0xFF, int & 0xFF,255)
        case 8: // ARGB (32-bit)
            (r, g, b, a) = (int >> 24, int >> 16 & 0xFF, int >> 8 & 0xFF, int & 0xFF)
        default:
            throw ColourParsingError.invalidInput("String is not a valid hex colour string: \(hexString)")
        }
        self.init(red: CGFloat(r) / 255, green: CGFloat(g) / 255, blue: CGFloat(b) / 255, alpha: CGFloat(a) / 255)
    }
}