Question

I have a custom coloured background that the user can choose, this however means when they change the colour, the label is invisible because it is the same as the background and I do not want this. The code I have is: opacityLabel.textColor = bgView.backgroundColor; In this bit of code the colour is the same at the start but doesn’t change when I adjust the background colour, I also need the colour to continually change with the background colour, I was wondering what I could replace with “=” to make the label do the opposite colour. I can’t do “!=” because that means is not equal to rather than opposite! If you can’t do it this way could you provide me with a way of doing it?

Answer 1

The first thing you’ll need to do is calculate the opposite colour to the backgroundColor, and then assign it to the textColor property.

To do this you’ll need to use the getRed:green:blue:alpha: method on backgroundColor. This will give you values between 0.0 and 1.0 for each component of your colour.
Then use the UIColor class method colorWithRed:green:blue:alpha: to create a new UIColor, but use (1.0 – component value) for each of the components.

Then finally assign your new colour to opacityLabel.textColor