It looks like you've declared the method, but never actually implemented it!
What's your .m file look like?
On 30 Mar 2011, at 03:33, Nik Heger wrote:
> I am new to Objective-C so please forgive me if this is obvious.
>
> I come from Ruby, where extending built in classes is straight forward - you
> do it, and it works. I expected the same in Obj-C but got a confusing
> result: It works sometimes, but not others.
>
> Here is what I did:
>
> 1 - Created a Category on NSObject, this is the header, implementation was
> working and tested too (and pretty simple)
>
> @interface NSObject (Logger)
>
> - (void) LOGx1: (id) first, ...;// support for simple logging of multiple
> string
>
> @end
>
> So now, I expected to be able to call LOGx1 on any object
>
> 2 - Tried this out on a String object and on my UIViewController subclass
> which gets loaded from a nib file
>
> // FirstViewController.m - subclass of UIViewController, loaded from a nib
>
> #import "NSObject-Logger.h"
> ...
>
> - (void)sample
>
> {
>
> NSString *test = @"A TEST";
>
> [test LOGx1: @"Testing NSString!",nil]; // working
>
> [self LOGx1: @"foobar ",nil]; // throwing exception
>
> }
>
> The first invocation works as expected. Seems like NSString knows about the
> Logger category. The second one crashes with an unknown selector. The stack
> trace seems to indicate that my FirstViewController class inherits from
> NSObject(NSObject) instead of NSObject(Logger). Output and stack trace in
> [1].
>
> That's as far as I got. Question is, why?
>
> I tried the -ObjC and the -all_load linking flags after Googling for the
> issue - didn't make a difference.
>
> The thing I don't understand is: If I define a category on a built-in
> object, I expect it to work under all circumstances. If it doesn't work for
> some, it would be rather pointless to have this facility, no? Is there
> anything obvious I am missing? Does it have to do with the NIB/XIB loading?
>
> thanks, sorry for the length...
>
> ~Nik
>
> PS: I later realized logging as a Category makes no sense and moved it into
> its own Logger class where it's a class method; but I still want to
> understand categories.
>
> [1]
> Here is what I get for the stack trace:
>
> *2011-03-30 09:18:52.802 xxx[23245:207] Testing NSString!*
>
> *2011-03-30 09:18:52.803 xxx[23245:207] -[FirstViewController LOGx1:]:
> unrecognized selector sent to instance 0x4d37f30*
>
> *2011-03-30 09:18:52.805 xxx[23245:207] *** Terminating app due to uncaught
> exception 'NSInvalidArgumentException', reason: '-[FirstViewController
> LOGx1:]: unrecognized selector sent to instance 0x4d37f30'*
>
> **** Call stack at first throw:*
>
> *(*
>
> * 0 CoreFoundation 0x00e935a9 __exceptionPreprocess +
> 185*
>
> * 1 libobjc.A.dylib 0x00fe7313 objc_exception_throw +
> 44*
>
> * 2 CoreFoundation 0x00e950bb -[NSObject(NSObject)
> doesNotRecognizeSelector:] + 187*
> *
> *
> *
> *
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