Extracting hex value from NSColor

By Michael Robinson on December 6, 2011, Filed in: Cocoa | Objective C
Example project available on GitHub –

NSColor+Hex category available on GitHub –

This category on NSColor allows one to get or set an NSColor’s colour using hex values. Intitialising an NSColor with a hexadecimal colour: 
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@try {
    // Both shorthand and full forms of hexadecimal colours are accepted
    [colorWell setColor:[NSColor colorWithHex:@"#F00"]];
    [colorWell setColor:[NSColor colorWithHex:@"#Ff0000"]];
}
@catch (NSException *exception) {
    NSLog(@"%@", [exception description]);
}
It’ll throw an exception if one attempts to use a string that is not 3 or 6 characters in length, excluding the hash. Getting the hexadecimal representation of a given NSColor: 
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NSString *hexColor = [color hexColor]
This being my first Cocoa category, I’m sure it must have rough edges. Nevertheless, I have found it very useful. Below is the header for NSColor+Hex: 
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//
//  NSColor+Hex.h
//  CINSColor+Hex
//
//  Created by Michael Robinson on 4/12/11.
//  Copyright 2011 Code of Interest. All rights reserved.
//
 
#import <AppKit/AppKit.h>
 
@interface NSColor (Hex)
 
+ (NSColor *) colorWithHex:(NSString *)hexColor;
- (NSString *) hexColor;
 
@end
And the implementation, more verbose than I’d like but it does the job. If anyone improves on it, I’ll be happy to update this page & accept your pull request on GitHub: 
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//
//  NSColor+Hex.m
//  CINSColor+Hex
//
//  Created by Michael Robinson on 4/12/11.
//  Copyright 2011 Code of Interest. All rights reserved.
//
 
#import "NSColor+Hex.h"
 
@implementation NSColor (Hex)
 
 
+ (NSColor *) colorWithHex:(NSString *)hexColor {
 
    // Remove the hash if it exists
    hexColor = [hexColor stringByReplacingOccurrencesOfString:@"#" withString:@""];
    int length = (int)[hexColor length];
    bool triple = (length == 3);
 
    NSMutableArray *rgb = [[NSMutableArray alloc] init];
 
    // Make sure the string is three or six characters long
    if (triple || length == 6) {
 
        CFIndex i = 0;
        UniChar character = 0;
        NSString *segment = @"";
        CFStringInlineBuffer buffer;
        CFStringInitInlineBuffer((CFStringRef)hexColor, &buffer, CFRangeMake(0, length));
 
 
        while ((character = CFStringGetCharacterFromInlineBuffer(&buffer, i)) != 0 ) {
            if (triple) segment = [segment stringByAppendingFormat:@"%c%c", character, character];
            else segment = [segment stringByAppendingFormat:@"%c", character];
 
            if ((int)[segment length] == 2) {
                NSScanner *scanner = [[NSScanner alloc] initWithString:segment];
 
                unsigned number;
 
                while([scanner scanHexInt:&number]){
                    [rgb addObject:[NSNumber numberWithFloat:(float)(number / (float)255)]];
                }
                segment = @"";
            }
 
            i++;
        }
 
        // Pad the array out (for cases where we're given invalid input)
        while ([rgb count] != 3) [rgb addObject:[NSNumber numberWithFloat:0.0]];
 
        return [NSColor colorWithCalibratedRed:[[rgb objectAtIndex:0] floatValue] 
                                         green:[[rgb objectAtIndex:1] floatValue] 
                                          blue:[[rgb objectAtIndex:2] floatValue] 
                                         alpha:1];
    }
    else {
        NSException* invalidHexException = [NSException exceptionWithName:@"InvalidHexException"
                                                                   reason:@"Hex color not three or six characters excluding hash"                                    
                                                                 userInfo:nil];
        @throw invalidHexException;
 
    }
 
}
 
- (NSString *) hexColor {
     if ([[self colorSpaceName] isEqualToString:NSCalibratedWhiteColorSpace]) {
        return [NSString stringWithFormat:@"#%0.2X%0.2X%0.2X",
            (int)(r * [self whiteComponent]),
            (int)(g * [self whiteComponent]),
            (int)(b * [self whiteComponent])];
    }
    else if ([[self colorSpaceName] isEqualToString:NSCalibratedBlackColorSpace]) {
        return [NSString stringWithFormat:@"#%0.2X%0.2X%0.2X",
            (int)(r * [self blackComponent]),
            (int)(g * [self blackComponent]),
            (int)(b * [self blackComponent])];
    }
    else if ([[self colorSpaceName] isEqualToString:NSCalibratedRGBColorSpace]
             || [[self colorSpaceName] isEqualToString:NSDeviceRGBColorSpace]) {
        return [NSString stringWithFormat:@"#%0.2X%0.2X%0.2X",
            (int)(r * [self redComponent]),
            (int)(g * [self blueComponent]),
            (int)(b * [self greenComponent])];
    }
    return @"transparent";
}
 
@end

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