对UIColor的取色封装

//hex填写十六进制值
#define COLOR_WITH_HEX(hexValue)     [UIColor colorWithRed:((float)((hexValue & 0xFF0000) >> 16)) / 255.0 green:((float)((hexValue & 0xFF00) >> 8)) / 255.0 blue:((float)(hexValue & 0xFF)) / 255.0 alpha:1.0f]
//hex填写十六进制值
+(UIColor*)colorWithRGB:(NSUInteger)hex
                  alpha:(CGFloat)alpha
{
    float r, g, b, a;
    a = alpha;
    b = hex & 0x0000FF;
    hex = hex >> 8;
    g = hex & 0x0000FF;
    hex = hex >> 8;
    r = hex;
    
    return [UIColor colorWithRed:r/255.0f green:g/255.0f blue:b/255.0f alpha:a];
}
//hexString填写十六进制字符串
+ (UIColor *)colorWithHexString:(NSString *)hexString {
    return [UIColor colorWithHexString:hexString alpha:1.0];
}
//hexString填写十六进制字符串
+ (UIColor *)colorWithHexString:(NSString *)hexString alpha:(CGFloat)alpha {
    if ([hexString hasPrefix:@"0x"] || [hexString hasPrefix:@"0X"]) {
        hexString = [hexString substringFromIndex:2];
    } else if ([hexString hasPrefix:@"#"]) {
        hexString = [hexString substringFromIndex:1];
    }
    
    unsigned int value = 0;
    BOOL flag = [[NSScanner scannerWithString:hexString] scanHexInt:&value];
    if(NO == flag)
        return [UIColor clearColor];
    float r, g, b, a;
    a = alpha;
    b = value & 0x0000FF;
    value = value >> 8;
    g = value & 0x0000FF;
    value = value >> 8;
    r = value;
    
    return [UIColor colorWithRed:r/255.0f green:g/255.0f blue:b/255.0f alpha:a];
}