How do I get list of all classes conform to certain protocol in Xcode 4?

Protocol *protocol = @protocol(YourProtocol);

int numberOfClasses = objc_getClassList(NULL, 0);
Class *classList = malloc(numberOfClasses * sizeof(Class));
numberOfClasses = objc_getClassList(classList, numberOfClasses);

for (int idx = 0; idx < numberOfClasses; idx++) 
{
    Class class = classList[idx];
    if (class_getClassMethod(class, @selector(conformsToProtocol:)) && [class conformsToProtocol:protocol])
    {
        NSLog(@"%@", NSStringFromClass(class));
    }
}
free(classList);

Use the Objective-C runtime functions.

• objc_getClassList to get the list of Classes
• class_getSuperclass or the -superclass method to walk the superclass chain
• class_conformsToProtocol or the -conformsToProtocol: method to check if a class conforms to a protocol