Question

I want to be able to store a backgroundcolor for a panel in my application in the database.

The value can be either a concrete color or empty, indicating it has been inherited from the parent.

I wanted to store this in an int-field that is non-nullable, by calling the System.Drawing.Color.ToArgb() method.

The return value of this method seems to be -1 for white, and -16777216 for black…

So I was thinking that for indicating the no color has been selected, I could store a positive integer. This would offer a very simple way to check whether an explicit color has been stored or no color has been stored.

Now I was wondering whether there is a legimitate reason why System.Drawing.Color.ToArgb() could ever return positive values. (What’s the range of possible return values for this function).

I haven’t been tampering around with the alpha channel, so I don’t know whether that would have influence….

If I’m not able to store a positive integer to indicate the abscence of an explicit color, I guess I will just have to make the field nullable….

Answer 1

Well, you get a 32-bit integer containing Alpha, Red, Green and Blue, each of them filling 8 bits.

The alpha value is in the highest-order 8 bits so for every non-transparent color you have those at 0xFF (which automatically makes that integer negative, if it’s a signed integer).

So if your alpha value drops below 128 (0x80) you will get positive color values.

The range of possible return values for that function is indeed 0x00000000 to 0xFFFFFFFF, in other words: every possible 32-bit integer. For a signed int this is −2147483648 to [phone].

In your case I’d definitely go with allowing NULL values, since that’s actually what you want here. If you drop the alpha value altogether you have another 8 bits for information, though. So you could then implement it checking for negative/non-negative values.