The runtime sendsinitializeto 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.) The runtime sends the initialize message to classes in a thread-safe manner.Superclasses receive this message before their subclasses.


Theloadmessage 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.

The order of initialization is as follows:

All initializers in any framework you link to.

All+loadmethods in your image.

All C++ static initializers and C/C++__attribute__(constructor)functions in your image.

All initializers in frameworks that link to you.

In addition:

A class’s+loadmethod is called after all of its superclasses’+loadmethods.

A category+loadmethod is called after the class’s own+loadmethod.

In a custom implementation ofloadyou can therefore safely message other unrelated classes from the same image, but anyloadmethods implemented by those classes may not have run yet.