[iOS] [Objective-C] Helper method to convert hex representation of the color to UIColor

HexToColor

@interface UIColor (Hex)

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

@end

@implementation UIColor (Hex)

+ (UIColor *)colorWithHexString:(NSString *)hex
{
    NSString *colorString = [[hex 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", hex];
            
            break;
        }
    }
    
    return [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
}

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

@end