Create a class at runtime - Why do NSClassFromString AND objc_getclass return nil ?

Question

I've tried using both:

NSClassFromString and objc_getclass

to return a class, so I can create it at runtime, but both functions return nil for some classes, for example "TestClass". Note that NSClassFromString works for me for 99% of classes.

If I add

[TestClass class];

before I call NSStringFromClass or objc_getclass it, it works. and if I try to just create the class using a class reference, i.e.:

[TestClass alloc];

it works too. So how can I force the class to load at runtime so NSClassFromString or objc_getclass will not return nil?

Answer 1

The Objective-C Runtime Reference can help you here. For example, the documentation for objc_getClass says, "The Class object for the named class, or nil if the class is not registered with the Objective-C runtime." Looking around for discussion of registration you find this tidbit in objc_getClassList: "The Objective-C runtime library automatically registers all the classes defined in your source code. You can create class definitions at runtime and register them with the objc_addClass function." (And of course the docs are out of date because objc_addClass is deprecated, objc_allocateClassPair and objc_registerClassPair in its place.)

This looks like a world of hurt if you don't make this easy on yourself. Any chance you can just reference your dynamic classes in code when the app starts?