What kind of category methods do you use to make Cocoa programming easier?

Question

I use a collection of category methods for Cocoa's built in classes to make my life easier. I'll post some examples, but I really want to see what other coders have come up with. What kind of handy category methods are you using?

Example #1:

@implementation NSColor (MyCategories)
+ (NSColor *)colorWithCode:(long)code
{
    return [NSColor colorWithCalibratedRed:((code & 0xFF000000) >> 24) / 255.0
                                     green:((code & 0x00FF0000) >> 16) / 255.0
                                      blue:((code & 0x0000FF00) >>  8) / 255.0
                                     alpha:((code & 0x000000FF)      ) / 255.0];
}
@end

// usage:
NSColor * someColor = [NSColor colorWithCode:0xABCDEFFF];

Example #2:

@implementation NSView (MyCategories)
- (id)addNewSubViewOfType:(Class)viewType inFrame:(NSRect)frame
{
    id newView = [[viewType alloc] initWithFrame:frame];
    [self addSubview:newView];
    return [newView autorelease];
}
@end

// usage:
NSButton * myButton = [someView addNewSubviewOfType:[NSButton class]
                                            inFrame:someRect];

Answer 1

I've really been loving Andy Matuschak's "KVO+Blocks" category on NSObject. (Yes, it adds some new classes internally as implementation details, but the end result is just a category on NSObject). It lets you provide a block to be executed when a KVO-conforming value changes rather than having to handle every KVO observation in the observeValueForKeyPath:ofObject:change:context: method.

Answer 2

Regular Expressions with RegexKitLite. Download @ RegexKitLite-3.1.tar.bz2

Answer 3

Category, which adds md5/sha1 hashing to NSString. NSData one is similar.

#define COMMON_DIGEST_FOR_OPENSSL
#import <CommonCrypto/CommonDigest.h>


@implementation NSString(GNExtensions)

    - (NSString*)
    hashMD5
    {
        NSData* data = [self dataUsingEncoding: NSUTF8StringEncoding allowLossyConversion: NO];

        unsigned char hashingBuffer[16];
        char outputBuffer[32];

        CC_MD5([data bytes], [data length], hashingBuffer);

        for(int index = 0; index < 16; index++)
        {
            sprintf(&outputBuffer[2 * index], "%02x", hashingBuffer[index]);
        }

        return([NSString stringWithCString: outputBuffer length: 32]);
    }


    - (NSString*)
    hashSHA1
    {
        NSData* data = [self dataUsingEncoding: NSUTF8StringEncoding allowLossyConversion: NO];

        unsigned char hashingBuffer[20];
        char outputBuffer[40];

        CC_SHA1([data bytes], [data length], hashingBuffer);

        for(int index = 0; index < 20; index++)
        { 
            sprintf(&outputBuffer[2 * index], "%02x", hashingBuffer[index]);
        }

        return([NSString stringWithCString: outputBuffer length: 40]);
    }


@end