Objective-C Method Parameters Problem

Question

I'm attempting to define an extremely simple utility method that will save me from having to use a calculator to define RGB values as percentages. When I look into Apple's sample code called "QuartzCache", in the DrawView.m file, line 96, I see this:

float whiteColor[4] = {1, 1, 1, 1};

However, when I attempt to created a method like the following, the compiler hates me. A half-hour of intensive Googling has not produced any help.

 +(float[])percentagesRGBArray:(float[])rgbArray{

        float red = rgbArray[0];
        float green = rgbArray[1];
        float blue = rgbArray[2];
        float alpha = rgbArray[3];
        red = red/255;
        green = green/255;
        blue = blue/255;
        alpha = alpha;
        float percentagesRGBArray[4] = {red, green, blue, alpha};


        return  percentagesRGBArray;
    }

What is the proper way to define such a method? What am I doing wrong here?

Answer 1

Define a struct that contains all of the components, or wrap up each individual component in an NSNumber. Alternatively, use an NSColor instance to contain your colour components.

• struct way:

  typedef struct
  {
      float red;
      float green;
      float blue;
      float alpha;
  } MyColor;
  
  - (MyColor) percentagesRGBArray:(MyColor) incoming
  {
      MyColor result;
      result.red = incoming.red / 255;
      result.green = incoming.green / 255;
      result.blue = incoming.blue / 255;
      result.alpha = incoming.alpha;
      return result;
  }
  

• NSNumber way:

  - (NSArray *) percentagesRGBArray:(float[]) rgbArray
  {
      NSNumber *red = [NSNumber numberWithFloat:rgbArray[0] / 255];
      NSNumber *green = [NSNumber numberWithFloat:rgbArray[1] / 255];
      NSNumber *blue = [NSNumber numberWithFloat:rgbArray[2] / 255];
      NSNumber *alpha = [NSNumber numberWithFloat:rgbArray[3]];
  
      return [NSArray arrayWithObjects:red, green, blue, alpha, nil];
  }
  

• NSColor way:

  - (NSColor *) percentagesRGBArray:(float[]) rgbArray
  {
      CGFloat red = rgbArray[0] / 255;
      CGFloat green = rgbArray[1] / 255;
      CGFloat blue = rgbArray[2] / 255;
      CGFloat alpha = rgbArray[3];
  
      return [NSColor colorWithDeviceRed:red
                                   green:green
                                    blue:blue
                                   alpha:alpha];
  }