UIColor+HexString.m

//
//  UIColor+HexString.m
//  Pegasus
//
//  Created by Micah Hainline
//  http://stackoverflow.com/users/590840/micah-hainline
//

#import "UIColor+HexString.h"

@interface UIColor()

+ (CGFloat)colorComponentFrom:(NSString *) string start: (NSUInteger) start length: (NSUInteger) length;

@end

@implementation UIColor (HexString)

+ (UIColor *)colorWithHexString:(NSString *)hexString {
    NSString *colorString = [[hexString stringByReplacingOccurrencesOfString:@"#" withString:@""] uppercaseString];
    CGFloat alpha, red, blue, green;
    switch ([colorString length]) {
        case 3: // #RGB
            alpha = 1.0f;
            red   = [self colorComponentFrom:colorString start:0 length:1];
            green = [self colorComponentFrom:colorString start:1 length:1];
            blue  = [self colorComponentFrom:colorString start:2 length:1];
            break;
        case 4: // #ARGB
            alpha = [self colorComponentFrom:colorString start:0 length:1];
            red   = [self colorComponentFrom:colorString start:1 length:1];
            green = [self colorComponentFrom:colorString start:2 length:1];
            blue  = [self colorComponentFrom:colorString start:3 length:1];          
            break;
        case 6: // #RRGGBB
            alpha = 1.0f;
            red   = [self colorComponentFrom:colorString start:0 length:2];
            green = [self colorComponentFrom:colorString start:2 length:2];
            blue  = [self colorComponentFrom:colorString start:4 length:2];                      
            break;
        case 8: // #AARRGGBB
            alpha = [self colorComponentFrom:colorString start:0 length:2];
            red   = [self colorComponentFrom:colorString start:2 length:2];
            green = [self colorComponentFrom:colorString start:4 length:2];
            blue  = [self colorComponentFrom:colorString start:6 length:2];                      
            break;
        default:
            [NSException raise:@"Invalid color value" format:@"Color value %@ is invalid.  It should be a hex value of the form #RBG, #ARGB, #RRGGBB, or #AARRGGBB", hexString];
            break;
    }
    return [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
}

+ (CGFloat)colorComponentFrom:(NSString *)string start:(NSUInteger)start length:(NSUInteger)length {
    NSString *substring = [string substringWithRange: NSMakeRange(start, length)];
    NSString *fullHex = length == 2 ? substring : [NSString stringWithFormat: @"%@%@", substring, substring];
    unsigned hexComponent;
    [[NSScanner scannerWithString: fullHex] scanHexInt:&hexComponent];
    return hexComponent / 255.0;
}

@end