Implementing ClassCategories

This sample code comes from a mailing list post by Uli Zappe and shows how to implement ClassCategories:

MySillyStringAddition.h

#import <Foundation/NSString.h>

@interface NSString (MySillyStringAddition)

• (NSString *)sillyMethodThatReturnHello;

@end

MySillyStringAddition.m

#import “MySillyStringAddition.h”

@implementation NSString (MySillyStringAddition)

• (NSString *)sillyMethodThatReturnHello { return @”Hello”; }

@end

---

See also KissyFaceView for an example of hiding private API using ClassCategories. You may also want to see CocoaDevUsersAdditions for more keen categories.

I’m not sure of the value of this example but it was meant to serve as an example of what could usefully? be done, it’s based on some SmallTalk code I once saw.

URLString.h

Add a Category so that a NSString can return the contents of a Web page as NSString.

#import <Foundation/NSString.h>

@interface NSString (asURL)

• (NSString *)asURL; @end

URLString.m

#import <Foundation/Foundation.h> #import “URLString.h” @implementation NSString (asURL)

• (NSString *)asURL { NSURL *url = [NSURL URLWithString: self ]; NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL: url cachePolicy: NSURLRequestReloadIgnoringCacheData timeoutInterval: 10];

  NSURLResponse *response; NSError *error; NSData *data = [NSURLConnection sendSynchronousRequest: request returningResponse: &response error: &error];

  NSString *output = [NSString stringWithCString:[data bytes] length:[data length]];

  if (error) { NSLog(@”%@”, error); }

  return [output autorelease]; } @end

main.m

Example of silly use.

#import <Foundation/Foundation.h> #import “URLString.h” int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = NSAutoreleasePool alloc] init];

NSString *page = [@”http://www.google.com” asURL]; NSLog(@”Page = %@”, page);

[pool release]; return 0; }

Ahh, [[StringWithCString strikes again! Please don’t use it, it is evil.

Category:CocoaDevUsersAdditions