Frameworks for static libraries xcode

3
votes

I have just added a linked library to my project using the question here Process for linking static ObjC libraries in XCode and the document linked to in the answer.

I happen to know the library uses CoreData objects, like NSManagedObject, although in the library's xcode project the CoreData framework isn't added and it builds with no errors. However when I build my app it comes up with several errors such as:

Undefined symbols:
"_OBJC_CLASS_$_NSManagedObject", referenced from:
  _OBJC_CLASS_$_AClass in library.a(AClass.o)

So seeing as all the errors mentioned CoreData objects, I added the CoreData framework to my app and it built successfully. So now I tried remove CoreData framework from my app and added it the libraries project and them built both and it failed.

So why does it work when I have coredata added in my project but not in the libraries project, and only the library uses it?

(and why does the library build without needing the coredata framework on its own?)

2
objective-cxcodestatic-libraries

2 Answers

4
votes

The library is static. It is not a stand-alone piece of code, it must be linked.

Your application is linked, which means the linker resolves all the external dependencies and fills in the library functions' addresses in the final executable.

If you want to use a library that has a Core Data dependency in your application, you must link against Core Data.framework.

Adding a linking stage to a static library has no effect, since there is no linker involved in creating a static library, only a compiler (and an archiver).

0
votes

Now, the problem can sometimes be avoided by using the new @import syntax in your libraries header file. The compiler will then automatically link against the used framework, even if you use a static library.