将16进制字符串或者整型转换成 UIColor

UIColor+Utils.swift

//
//  UIColor+Utils.swift
//
//  Created by Yozone Wang on 15/12/17.
//  Copyright © 2015年 Yozone Wang. All rights reserved.
//

import UIKit

private let UIColorCache = NSCache()

private func intToColorComponent(intValue: UInt) -> CGFloat {
    return CGFloat(intValue) / 255
}

extension UIColor {
    /**
     将 16 进制字符串转换成 UIColor，支持的格式有 RGB，RGBA，RRGGBB，RRGGBBAA，字符串可以有 # 或者 0x 前缀

     - parameter hexString: 16 进制字符串

     - returns: 转换后的 UIColor，如果不符合说明中的格式，则初始化失败，返回 nil
     */
    convenience init?(hexString: String) {
        var mutableString = hexString
        if mutableString.hasPrefix("#") {
            mutableString.removeAtIndex(mutableString.startIndex)
        }
        if mutableString.hasPrefix("0x") {
            mutableString.removeRange(mutableString.startIndex..<mutableString.startIndex.advancedBy(2))
        }

        if let color = UIColorCache.objectForKey(mutableString) as? UIColor {
            self.init(CGColor: color.CGColor)
            return
        }

        guard let _ = mutableString.rangeOfString("^[0-9a-f]{3,8}$", options: [.RegularExpressionSearch, .CaseInsensitiveSearch]) else {
            return nil
        }

        let redString: String, greenString: String, blueString: String, alphaString: String
        switch mutableString.characters.count {
        case 3:
            redString = String(count: 2, repeatedValue: mutableString[mutableString.startIndex])
            greenString = String(count: 2, repeatedValue: mutableString[mutableString.startIndex.advancedBy(1)])
            blueString = String(count: 2, repeatedValue: mutableString[mutableString.startIndex.advancedBy(2)])
            alphaString = "FF"
        case 4:
            redString = String(count: 2, repeatedValue: mutableString[mutableString.startIndex])
            greenString = String(count: 2, repeatedValue: mutableString[mutableString.startIndex.advancedBy(1)])
            blueString = String(count: 2, repeatedValue: mutableString[mutableString.startIndex.advancedBy(2)])
            alphaString = String(count: 2, repeatedValue: mutableString[mutableString.startIndex.advancedBy(3)])
        case 6:
            redString = mutableString[mutableString.startIndex..<mutableString.startIndex.advancedBy(2)]
            greenString = mutableString[mutableString.startIndex.advancedBy(2)..<mutableString.startIndex.advancedBy(4)]
            blueString = mutableString[mutableString.startIndex.advancedBy(4)..<mutableString.startIndex.advancedBy(6)]
            alphaString = "FF"
        case 8:
            redString = mutableString[mutableString.startIndex..<mutableString.startIndex.advancedBy(2)]
            greenString = mutableString[mutableString.startIndex.advancedBy(2)..<mutableString.startIndex.advancedBy(4)]
            blueString = mutableString[mutableString.startIndex.advancedBy(4)..<mutableString.startIndex.advancedBy(6)]
            alphaString = mutableString[mutableString.startIndex.advancedBy(6)..<mutableString.startIndex.advancedBy(8)]
        default:
            return nil
        }

        let red = intToColorComponent(UInt(redString, radix: 16) ?? 0)
        let green = intToColorComponent(UInt(greenString, radix: 16) ?? 0)
        let blue = intToColorComponent(UInt(blueString, radix: 16) ?? 0)
        let alpha = intToColorComponent(UInt(alphaString, radix: 16) ?? 0)
        self.init(red: red, green: green, blue: blue, alpha: alpha)

        UIColorCache.setObject(self, forKey: mutableString)
    }

    /**
     将 32 位整型转换成 `UIColor`

     - parameter intValue:  UIColor 的 32 位整型数值，顺序为 RGBA，如果 intValue 小于等于 0xFFFFFF 则 alpha 值为 1

     - returns: 转换后的 `UIColor`
     */
    convenience init(intValue: UInt) {
        if let color = UIColorCache.objectForKey(intValue) as? UIColor {
            color
            self.init(CGColor: color.CGColor)
            return
        }

        let red: CGFloat
        let green: CGFloat
        let blue: CGFloat
        let alpha: CGFloat
        if intValue > 0xFFFFFF {
            red = intToColorComponent((intValue >> 24) & 0xFF)
            green = intToColorComponent((intValue >> 16) & 0xFF)
            blue = intToColorComponent((intValue >> 8) & 0xFF)
            alpha = CGFloat(intValue & 0xFF) / 255
        } else {
            red = intToColorComponent((intValue >> 16) & 0xFF)
            green = intToColorComponent((intValue >> 8) & 0xFF)
            blue = intToColorComponent(intValue & 0xFF)
            alpha = 1
        }
        self.init(red: red, green: green, blue: blue, alpha: alpha)

        UIColorCache.setObject(self, forKey: intValue)
    }
}