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iOS

Posted by Kevin Hamil
Kevin Hamil
8,203 Points

Converting RGB to hex Numeric Value

Here's a snippet of code I'm having trouble with... It generates random R, G and B components separately based on 0-255, but issue is whenever one (or more) of the parts generate within the first 16 values (0-15). That value will only display one of the two places within the hex string.

For example, if green generated a value of 9, the hex string would look like "A7 9B3"... missing the 3rd place value. It looks like the color outputs correctly.. it's just the string that is not displaying correctly.

I'm sure it's something simple and I've tried to figure it out, but I don't think I know what I should be looking for exactly.

Any help would be appreciated.

rgbRedValue = CGFloat(arc4random_uniform(256))
rgbGreenValue = CGFloat(arc4random_uniform(256))
rgbBlueValue = CGFloat(arc4random_uniform(256))

hexValue = String(format:"%2X", Int(rgbRedValue)) + String(format:"%2X", Int(rgbGreenValue)) + String(format:"%2X", Int(rgbBlueValue))

2 Answers

Stone Preston
Stone Preston
42,016 Points

ah, I see now. you can just specify to have a minimum width of 2 and pad it with zeroes using %02X:

let rgbRedValue = 200
let rgbGreenValue = 13
let rgbBlueValue = 45

let hexValue = String(format:"%02X", Int(rgbRedValue)) + String(format:"%02X", Int(rgbGreenValue)) + String(format:"%02X", Int(rgbBlueValue))
Kevin Hamil
Kevin Hamil
8,203 Points

Ahhh, you're awesome. Thank you.

I'm pretty new to Obj-C/Swift, so I have been wracking my brain trying to figure this out. I will have to go look up "padding" now so I have that in the vault. I actually tried putting the 0 before the % sign, but didn't think to try it after. Much appreciated!

Stone Preston
Stone Preston
42,016 Points
Stone Preston
Stone Preston
42,016 Points

looking at the String Format Specifiers, the hexadecimal format specifier is %X for capital letters. have you tried just %X instead of %2X. 

hexValue = String(format:"%X", Int(rgbRedValue)) + String(format:"%X", Int(rgbGreenValue)) + String(format:"%X", Int(rgbBlueValue))

I just tried the above in playgrounds and it seemed to work fine, whereas with %2X i did notice the empty space.

Kevin Hamil
Kevin Hamil
8,203 Points

Stone, thanks for answering. Let me clarify the question a bit. Your answer does remove the empty space, but I don't want to remove it, I want to fill it in. I guess by default, the compiler is dropping the leading "0" in the first 16 possible values (0-15). I want to somehow retain that leading "0" so the hexadecimal remains 6 place values.

Example of the problem...

  1. Generate random red, green and blue color components = 200, 13, 45
  2. Hex equivalent = C80D2D
  3. Compiles as = C8 D2D (omitting the leading zero of the green value
  4. I assign the hex value to a label and it shows a missing value

I hope that better explains what I'm asking. Thanks.