About UIColor , is this a bug or something?

Question

I used to think [UIColor whiteColor] was exactly same as [UIColor colorWithRed:1 green:1 blue:1 alpha:1], but it turns out it's not! Can anyone explain this ?

CGFloat red1, green1, blue1, alpha1;
UIColor * color1 = [UIColor whiteColor];
[color1 getRed:&red1 green:&green1 blue:&blue1 alpha:&alpha1];
NSLog(@"%f, %f, %f, %f", red1, green1, blue1, alpha1);

UIColor * color2 = [UIColor colorWithRed:1 green:1 blue:1 alpha:1];
[color2 getRed:&red1 green:&green1 blue:&blue1 alpha:&alpha1];
NSLog(@"%f, %f, %f, %f", red1, green1, blue1, alpha1);

output:

0.000000, 0.000000, 0.000000, -1.998628
1.000000, 1.000000, 1.000000, 1.000000

This is uncool.. very unpleasent

rmaddy rmaddy · Accepted Answer · 2012-10-25T05:59:38

From the docs for UIColor getRed:green:blue:alpha::

If the color is in a compatible color space, the color is converted into RGB format and its components are returned to your application. If the color is not in a compatible color space, the parameters are unchanged.

[UIColor whiteColor] and shades of gray created with UIColor colorWithWhite:alpha: are from a different color space than the RGB color space. Therefore they are not in a compatible color space. So it is inappropriate to use UIColor getRed:green:blue:alpha: with such colors.

Try initializing the 4 CGFloat values and see what you get. If you set them all to zero, they should stay zero.

About UIColor , is this a bug or something?

1 Answers