UIColor Additions

UIColor+Additions.h

//
//  UIColor+Additions.h
//
//  Created by Anthony Mattox on 9/28/12.
//  Copyright (c) 2012 Friends of The Web. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface UIColor (Additions)

- (NSString *) hexString;
+ (UIColor *) colorWithHexString: (NSString *) hexString;

- (float) lightness;
- (BOOL) isTransparent;

@end

UIColor+Additions.m

//
//  UIColor+Additions.m
//  Colors
//
//  Created by Anthony Mattox on 9/28/12.
//  Copyright (c) 2012 Friends of The Web. All rights reserved.
//

#import "UIColor+Additions.h"

@implementation UIColor (Additions)

#pragma mark - Hexidecimal Colors

- (NSString *) hexString {
    const CGFloat *_color = CGColorGetComponents(self.CGColor);
    NSString *hex = [NSString stringWithFormat:@"#%02X%02X%02X", (int)(_color[0]*255.0), (int)(_color[1]*255.0), (int)(_color[2]*255.0)];
    return hex;
}

+ (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;
}

#pragma mark - Inferred Color Properties

- (float) lightness {
    const CGFloat *componentColors = CGColorGetComponents(self.CGColor);
    return ((componentColors[0] * 299) + (componentColors[1] * 587) + (componentColors[2] * 114)) / 1000;
}

- (BOOL) isTransparent {
    const CGFloat *componentColors = CGColorGetComponents(self.CGColor);
    if (componentColors[3] == 0) {
        return YES;
    }
    return NO;
}

@end