Re: Finding all subclasses of a class ?
Re: Finding all subclasses of a class ?
- Subject: Re: Finding all subclasses of a class ?
- From: glenn andreas <email@hidden>
- Date: Thu, 25 Aug 2005 09:16:26 -0500
On Aug 25, 2005, at 8:59 AM, Eric Morand wrote:
Is there a way to find all subclasses of a class ?
At runtime, I want to be able to find all subclasses of my custim
Class : EutopiaModule.
Here is what I'm doing :
int numClasses;
Class * classes = NULL;
classes = NULL;
numClasses = objc_getClassList(NULL, 0);
if( numClasses > 0 )
{
classes = malloc( sizeof(Class) * numClasses );
(void) objc_getClassList( classes, numClasses );
}
int i;
for (i = 0; i < numClasses; i++ )
{
if ( [classes[i] respondsToSelector:@selector
(isSubclassOfClass:)] )
{
if ( [classes[i] isSubclassOfClass:[EutopiaModule
class]] )
{
NSLog (NSStringFromClass(classes[i]));
}
}
}
It doesn't work. The app crash with the following messages :
2005-08-25 15:57:10.104 €utopia[11296] *** +[Object
respondsToSelector:]: warning: Object compatibility method has been
executed at least once. Convert source code off it NOW!
2005-08-25 15:57:10.108 €utopia[11296] AccountsTransactionsModule
2005-08-25 15:57:10.116 €utopia[11296] *** Selector
'respondsToSelector:' sent to dealloced instance 0xa2881c9c of
class UNKNOWN.
Break at '-[_NSZombie respondsToSelector:]' to debug.
2005-08-25 15:57:10.116 €utopia[11296] An uncaught exception was
raised
2005-08-25 15:57:10.116 €utopia[11296] *** Selector
'respondsToSelector:' sent to dealloced instance 0xa2881c9c of
class UNKNOWN.
Break at '-[_NSZombie respondsToSelector:]' to debug.
2005-08-25 15:57:10.116 €utopia[11296] *** Uncaught exception:
<NSGenericException> *** Selector 'respondsToSelector:' sent to
dealloced instance 0xa2881c9c of class UNKNOWN.
Break at '-[_NSZombie respondsToSelector:]' to debug.
The reason it is breaking is that you are running into a few legacy
support classes (namely, Object and any subclasses of Object). You
then use "respondsToSelector" which isn't directly implemented for
Object (which is why you get the "Object compatibility method"
warning). There are other problems with a few other classes that
exist that aren't subclasses of NSObject (or don't implement the
NSObject protocol).
What is the right way to do this ?
Walk that superclass chain instead of using "isSubclassOfClass"
because that uses the runtime which is completely independent of
class hierarchy and any class specific methods.
See objc/objc-class.h for details, but something like this (typed in
mail and before I've finished morning coffee) :
struct objc_class *cls = (struct objc_class *)classes[i];
while (cls != NULL) {
if (cls == (struct objc_class *)[EutopiaModule class]) {
NSLog (@"%@",NSStringFromClass(classes[i]));
break;
}
cls = cls->super_class;
}
You should also never NSLog a "raw" variable/expression (i.e.,
without using a format string) because if it happened to contain a
format character, you'll probably crash.
Glenn Andreas email@hidden
<http://www.gandreas.com/> wicked fun!
Widgetarium | the quickest path to widgets
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