UIColor值和颜色的十六进制值（hex值）的互相转换

UIColor值是由4个0~1的值组成（Red，Green，Blue和Alpha值），而颜色的十六进制值（hex值）是一个十六进制数。这份代码是这两个值直接的互相转换。

+ (UIColor*) colorWithHex:(NSInteger)hexValue alpha:(CGFloat)alphaValue
{
    return [UIColor colorWithRed:((float)((hexValue & 0xFF0000) >> 16))/255.0
                           green:((float)((hexValue & 0xFF00) >> 8))/255.0
                            blue:((float)(hexValue & 0xFF))/255.0 alpha:alphaValue];
}

+ (UIColor*) colorWithHex:(NSInteger)hexValue
{
    return [UIColor colorWithHex:hexValue alpha:1.0];
}

+ (NSString *) hexFromUIColor: (UIColor*) color {
    if (CGColorGetNumberOfComponents(color.CGColor) < 4) {
        const CGFloat *components = CGColorGetComponents(color.CGColor);
        color = [UIColor colorWithRed:components[0]
                                green:components[0]
                                 blue:components[0]
                                alpha:components[1]];
    }

    if (CGColorSpaceGetModel(CGColorGetColorSpace(color.CGColor)) != kCGColorSpaceModelRGB) {
        return [NSString stringWithFormat:@"#FFFFFF"];
    }

    return [NSString stringWithFormat:@"#XXX", (int)((CGColorGetComponents(color.CGColor))[0]*255.0),
                                                        (int)((CGColorGetComponents(color.CGColor))[1]*255.0),
                                                        (int)((CGColorGetComponents(color.CGColor))[2]*255.0)];
}