Some libraries require the -all_load linker flag when linking to an Xcode project. However, this leads to a linker error if there are symbol conflicts among libraries. The
With Xcode 4, if you include the library project into your app project, then you can add this to the Other Linker Flags:
-force_load $(BUILT_PRODUCTS_DIR)/<library_name.a>
You still need the dependency, and you need to add the library in the Link Phase list of frameworks and libraries too.
EDIT: Apple now says as of some Xcode 4 release that you can simply use this linker flag: "-ObjC" to get libraries with categories to properly load. That flag is working just fine for me in Xcode 5. People are still up voting this answer, but I suspect that the -ObjC flag is the best solution now.
This worked for me. Like the above answers you still need to include the library in the project.
-force_load $(SRCROOT)/pathToLibraryFromProject/libname.a
For the path it's just the folders in your project that lead to where you put your library, for example BaseFoler/Subfolder/libName.a.