Traverse a class hierarchy from base to all descendants

Question

In an iOS app I am writing I want to traverse a class hierarchy to make an inventory of all subclasses. My intent is to use each subclass type as a key -- via NSStringForClass() -- in a dictionary.

My motivation is to be able to automatically discover all variants of a base class so that I can call methods associated with that class. For reasons of division of labor I prefer not to use method overriding here.

Is it possible to do such a traversal? How would it work?

Answer 1

Here's an example. This method will return all subclasses descending from the class you send the message to.

@interface NSObject (Debugging)

+ (NSArray *) allSubclasses;

@end

@implementation NSObject (Debugging)

+ (NSArray *) allSubclasses
{
    Class myClass = [self class];
    NSMutableArray *mySubclasses = [NSMutableArray array];

    unsigned int numOfClasses;
    Class *classes = objc_copyClassList(&numOfClasses);
    for (unsigned int ci = 0; ci < numOfClasses; ci++) {
        // Replace the code in this loop to limit the result to immediate subclasses:
        // Class superClass = class_getSuperclass(classes[ci]);
        // if (superClass == myClass)
        //  [mySubclasses addObject: classes[ci]];
        Class superClass = classes[ci];
        do {
            superClass = class_getSuperclass(superClass);
        } while (superClass && superClass != myClass);

        if (superClass)
            [mySubclasses addObject: classes[ci]];
    }
    free(classes);

    return mySubclasses;
}

@end

Modify it as needed, make recursive calls, etc.