将 16进制 装换为 RGB

很多时候都使用 #XXXXXX 这种16进制的颜色值，在ios中需要转换为 RGB

/// 转换 uicolor 颜色
func strConvertColor(colorStr:String , alpha:CGFloat = 1 ) -> UIColor {
    //删除字符串中的空格
    var str:String = colorStr.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet()).uppercaseString
    
    if str.hasPrefix("0X"){
        //如果是0x开头的，那么截取字符串，字符串从索引为2的位置开始，一直到末尾
        let index = str.startIndex.advancedBy(2)
        str = str.substringFromIndex(index)
    }else if str.hasPrefix("#"){
        //如果是#开头的，那么截取字符串，字符串从索引为1的位置开始，一直到末尾
        let index = str.startIndex.advancedBy(1)
        str = str.substringFromIndex(index)
    }
    if str.characters.count != 6 {
        return UIColor.clearColor()
    }
    
    let rString = (str as NSString).substringToIndex(2)
    let gString = ((str as NSString).substringFromIndex(2) as NSString).substringToIndex(2)
    let bString = ((str as NSString).substringFromIndex(4) as NSString).substringToIndex(2)
    
    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)
    
    return UIColor(red: CGFloat(r) / 255.0, green: CGFloat(g) / 255.0, blue: CGFloat(b) / 255.0, alpha: alpha )
}