Re: A question about categories

[Richard Frith-Macdonald]

On 5 May 2006, at 19:53, Vaisburd, Haim wrote:

> Hi,
>
> I would like to override a method of an existing class.
> One way is to create a category and define a method
> with the same name, e.g.
>
> @interface NSBitmapImageRep (MyCategory)
>  - destroy;
> @end
>
> Is there any way to call the original method
> within the implementation of my override,
> in this case the original [NSBitmapImageRep-destroy] ?

No.
Or not simply anyway.
What you can do is put your new implementation in a loadable bundle,  
then get the method implementation before loading that bundle.

eg.

// This is the code in the bundle
@implementation NSBitmapImageRep (MyCategory)
static IMP old;
+ (void) setOldImplementation: (IMP)imp
{
  old = imp;
}
- (void) destroy
{
  // new code here
  (*old)(self, @selector(destroy));     // Invoke old implementation
}
@end

// And this is the code to set it up
IMP oldMethod = [NSBitmapImageRep instancemethodForSelector: @selector 
(destroy)];
// load bundle here
[NSBitmapImageRep setOldImplementation: oldMethod];