Re: Categories
Re: Categories
- Subject: Re: Categories
- From: Shawn Erickson <email@hidden>
- Date: Sat, 4 May 2002 15:33:32 -0700
On Saturday, May 4, 2002, at 03:03 PM, email@hidden wrote:
I've created a category of NSMutableData, compiled it into a framework,
and am now trying to use it in an application. I've imported the
header file from the framework, and the application compiles fine. But
when I try to run it, I get these errors:
2002-05-04 18:01:34.507 Compressor[4006] *** -[NSConcreteMutableData
bzip2]: selector not recognized
2002-05-04 18:01:34.531 Compressor[4006] *** -[NSConcreteMutableData
bzip2]: selector not recognized
What's up with that? I thought I could just use the selectors added by
my category as if they were normal ones. Am I supposed to do something
special?
I haven't looked into NSMutableData myself but it is most likely part of
a class cluster. In a nut shell this means that when you use init an
NSMutableData object you get back a different type of object that
supports the same public messages that NSMutableData defines. So you
category is against NSMutableData not NSConcreteMutableData which
appears to be what you are really operating on when you attempt to send
the bzip2 message.
For more on the class cluster pattern see...
http://developer.apple.com/techpubs/macosx/Cocoa/TasksAndConcepts/ProgrammingTopics/
Foundation/Concepts/ClassClusters.html
-Shawn
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