How to generate a random UIColor? - ios

Question

I'm trying to generate a random colour from 8 options. All of the stack overflow posts / tutorials I've found have been ANY random colour. In my prefix.pch I defined 8 different sets of colour definitions this is a single example:
#define cola1 209/255.
#define colb1 0/255.
#define colc1 0/255.
#define cold1 1.0/255.
Defining different colour values for cola1-8, colb1-8, colc1-8, and cold1-8.
Then I set up a random number generator:
int randomNumber;
randomNumber = arc4random() %8;
randomNumber = randomNumber + 1;
whatRandomNumberIs = randomNumber;
I then tried setting up an [NSString stringWithFormat:#"cola%i", randomNumber]; inside the [UIColor colorWithRed etc]
like this:
[UIColor colorWithRed:[NSString stringWithFormat:#"cola%i", whatRandomNumberIs] green:[NSString stringWithFormat:#"colb%i", whatRandomNumberIs] blue:[NSString stringWithFormat:#"colc%i", whatRandomNumberIs] alpha:[NSString stringWithFormat:#"cold%i", whatRandomNumberIs]];
But then realised you cannot put an NSString in a CGFloat.
So now I'm stuck. How would I go about installing a random number from 1-8 inside the red, green, blue and alpha values without doing an NSString stringWithFormat? Is there another way to return a random UIColor value that is defined because I only want it to be specific colours??

Answer 1

Below is what you can do...
In prefix.pch you have as below.
#define colorCombination1 [UIColor colorWithRed:.... alpha:1.0];
#define colorCombination2 [UIColor colorWithRed:.... alpha:1.0];
#define colorCombination3 [UIColor colorWithRed:.... alpha:1.0];
#define colorCombination4 [UIColor colorWithRed:.... alpha:1.0];
#define colorCombination5 [UIColor colorWithRed:.... alpha:1.0];
#define colorCombination6 [UIColor colorWithRed:.... alpha:1.0];
#define colorCombination7 [UIColor colorWithRed:.... alpha:1.0];
#define colorCombination8 [UIColor colorWithRed:.... alpha:1.0];
Now you create array of this colors..
NSArray *myColorArray = [[NSArray alloc] initWithObjects:colorCombination1, colorCombination2, colorCombination3, colorCombination4, colorCombination5, colorCombination6, colorCombination7, colorCombination8, nil];
Now you get random number say variable as generatedRandomNumber.
UIColor *myRandomColor = [myColorArray objectAtIndex:generatedRandomNumber%8];
generatedRandomNumber%8 will give you remainder from the generatedRandomNumber.
Hope this is what you want.

Answer 2

Way you can get random color is by using hue , saturation and brightness
//random color
CGFloat hue = ( arc4random() % 256 / 256.0 ); // 0.0 to 1.0
CGFloat saturation = ( arc4random() % 128 / 256.0 ) + 0.5; // 0.5 to 1.0, away from white
CGFloat brightness = ( arc4random() % 128 / 256.0 ) + 0.5; // 0.5 to 1.0, away from black
UIColor *color = [UIColor colorWithHue:hue saturation:saturation brightness:brightness alpha:1];

Answer 3

You are trying to construct a string at runtime and then use it as the name of a macro that was defined at compile-time. That doesn't work. No information about the name of a compile-time macro is available at runtime.
Here is one correct way to choose a random color from a set defined at compile time. Define a method to return a random color, in a category on UIColor:
#interface UIColor (Liam_RandomColor)
+ (UIColor *)Liam_randomColor;
#end
Implement the method to first (one time only) initialize an array of the predefined colors, and second (every time) to return an element of the array at random:
#implementation UIColor (Liam_RandomColor)
+ (UIColor *)Liam_randomColor {
static dispatch_once_t onceToken;
static NSArray *colors;
dispatch_once(&onceToken, ^{
colors = #[
[UIColor colorWithRed:209/255.0 green:0 blue:0 alpha:1/255.0],
[UIColor colorWithRed:50/255.0 green:100/255.0 blue:100/255.0 alpha:1],
// etc.
];
});
return colors[arc4random_uniform(colors.count)];
}
#end

Answer 4

You could create a category on UIColor and wrap your predefined colors in a method, something similar to this:
#interface UIColor (myCategory)
+ (UIColor *)randomColorForInt(int n);
#end
#implementation
+ (UIColor *)randomColorForInt(int n) {
if (n == 0) {
return [UIColor colorWithRed:cola1 green:colb1 blue:colc1 alpha:cold1]];
}
...
}
#end