Objective C defining UIColor constants

I have a iPhone application with a few custom-defined colors for my theme. Since these colors will be fixed for my UI, I would like to define the colors in a class to be included (Constants.h and Constants.m). How do I do that? (Simply defining them do开发者_Python百科es not work because UIColors are mutable, and would cause errors - Initalizer not constant).

/* Constants.h */
extern UIColor *test;

/* Constants.m */
UIColor *test = [UIColor colorWithRed:1.0 green:1.0 blue:1.0 alpha:1.0];

Thanks!

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A UIColor is not mutable. I usually do this with colors, fonts and images. You could easily modify it to use singletons or have a static initializer.

@interface UIColor (MyProject)

+(UIColor *) colorForSomePurpose;

@end

@implementation UIColor (MyProject)

+(UIColor *) colorForSomePurpose { return [UIColor colorWithRed:0.6 green:0.8 blue:1.0 alpha:1.0]; }

@end

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For simplicity I did this:

/* Constants.h */
#define myColor [UIColor colorWithRed:255.0/255.0 green:255.0/255.0 blue:255.0/255.0 alpha:1.0]

Don't forget to leave out the ';' so you can use it as a normal expression.

I'm not sure if there's anything technically wrong with this approach, but it works fine, and avoids the compile-time constant initializer error - this code is effectively stuck in place anywhere you put 'myColor', so it doesn't ever get compiled until you actually use it.

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Another option

in your .h you can do

extern UIColor *  const COLOR_LIGHT_BLUE;

in your .mm you can do

UIColor* const COLOR_LIGHT_BLUE = [[UIColor alloc] initWithRed:21.0f/255 green:180.0f/255  blue:1 alpha:1];//;#15B4FF

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If you're looking for a quick and dirty one without extensions go with clang:

#define kGreenColor colorWithRed:(0/255.0) green:(213/255.0) blue:(90/255.0) alpha:1.0

- (void)doSomething
{
   _label.textColor = [UIColor kGreenColor];

}

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Often people put global constants into singleton objects - or as drawnonward noted, you can make them accessible via a class method of some class.

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Here's another way:

Header:

#if !defined(COLORS_EXTERN)
    #define COLORS_EXTERN extern
#endif

COLORS_EXTERN UIColor *aGlobalColor;

Implementation:

#define COLORS_EXTERN
#import "GlobalColors.h"


@interface GlobalColors : NSObject
@end

@implementation GlobalColors

+ (void)load
{
    aGlobalColor = [UIColor colorWithRed:0.2 green:0.3 blue:0.4 alpha:1];
}

@end

It's a bit of a hack, but you don't need to redefine the color in the implementation and you can access colors without a method call.

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Use the AppController to make the colors accessible globally, rather than a static variable. That way it makes sense from an architecture standpoint, and also if you wanted to hypothetically change color schemes, even while running, this would just be a method or two on the AppController