"The load message is sent to classes and categories that are both dynamically loaded and statically linked, but only if the newly loaded class or category implements a method that can respond."
So, the method will be called "automatically" upon load, but only if each subclass implements its own +load implementation, which probably is more trouble than you want. Also, there's no guarantee about the order +load calls are issued, so a subclass's +load might get called before its superclass's, and +load is considered bad performance juju, since it makes the system do work regardless of whether or not the application uses the class. +initialize doesn't have those problems, but it does have a different one -- notice the second sentence, quoting here from the +initialize documentation:
"The runtime sends initialize to each class in a program exactly one time just before the class, or any class that inherits from it, is sent its first message from within the program. (Thus the method may never be invoked if the class is not used.)"
That makes it unsuitable (or at least kind of risky) for the find-all- the-subclasses task originally described. objc_getClassList really is the right approach, though I'll note that caching the result doesn't work if new classes get loaded dynamically.
--Chris N. On Jun 18, 2008, at 10:24 AM, Jean-Daniel Dupas wrote:
IIRC, +initialize call the super implementation if the child class does not override it, but not the +load method that is called exactly once per class and per categorie.So +load will not be called automatically. Le 18 juin 08 à 18:57, Mike Abdullah a écrit :Another option would be to write a +load method in your abstract superclass that will be automatically called for any subclasses and register them with the superclass.Mike. On 18 Jun 2008, at 16:45, Laurent Cerveau wrote:Fantastic! Thanks to you and Omar. laurent On Jun 18, 2008, at 9:28 AM, Graham Cox wrote:If you need a list of subclasses of a class, there isn't a built- in function - you have to test them one at a time. However I had the exact same need recently and wrote a little helper class to do it. One thing I ran into in my situation is that I really needed to prevent +initialize from ever getting called, because some low-level classes in the Cocoa framework wrote certain messages to the log when they were invoked (because they are obsolete and shouldn't be used) but testing for the class itself was enough to trigger this.So, my code uses a lower-level function. Here it is: @interface DKRuntimeHelper : NSObject + (NSArray*) allClasses; + (NSArray*) allClassesOfKind:(Class) aClass; @end @implementation DKRuntimeHelper + (NSArray*) allClasses { return [self allClassesOfKind:[NSObject class]]; } + (NSArray*) allClassesOfKind:(Class) aClass {// returns a list of all Class objects that are of kind <aClass> or a subclass of it currently registered in the runtime. This caches the // result so that the relatively expensive run-through is only performed the first timestatic NSMutableDictionary* cache = nil; if ( cache == nil ) cache = [[NSMutableDictionary alloc] init]; // is the list already cached?NSArray* cachedList = [cache objectForKey:NSStringFromClass( aClass )];if ( cachedList != nil ) return cachedList; // if here, list wasn't in the cache, so build it the hard way NSMutableArray* list = [NSMutableArray array]; Class* buffer = NULL; Class cl; int i, numClasses = objc_getClassList( NULL, 0 ); if( numClasses > 0 ) { buffer = malloc( sizeof(Class) * numClasses ); NSAssert( buffer != nil, @"couldn't allocate the buffer"); (void) objc_getClassList( buffer, numClasses );// go through the list and carefully check whether the class can respond to isSubclassOfClass: - if so, add it to the list.for( i = 0; i < numClasses; ++i ) { cl = buffer[i]; if( classIsSubclassOfClass( cl, aClass )) [list addObject:cl]; } free( buffer ); } // save in cache for next time [cache setObject:list forKey:NSStringFromClass( aClass )]; return list; } @end BOOL classIsNSObject( const Class aClass ) {// returns YES if <aClass> is an NSObject derivative, otherwise NO. It does this without invoking any methods on the class being tested.return classIsSubclassOfClass( aClass, [NSObject class]); }BOOL classIsSubclassOfClass( const Class aClass, const Class subclass ){ Class temp = aClass; int match = -1;while(( 0 != ( match = strncmp( temp->name, subclass->name, strlen( subclass->name )))) && ( NULL != temp->super_class ))temp = temp->super_class; return ( match == 0 ); } hth, cheers, Graham On 18 Jun 2008, at 3:19 pm, Laurent Cerveau wrote:HiIs there a way to get all subclases of a class. I have a class that I would call abstract (although I did not find any real way to declare some methods as virtual) and would like to get a list of all "real" subclass implementations.Thanks laurent _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)Please do not post admin requests or moderator comments to the list.Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/graham.cox%40bigpond.com This email sent to [EMAIL PROTECTED]_______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. 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