Set the -ObjC Flag

You also need to add the -ObjC flag to Other Linker Flags.
  1. Select your project in the Project Navigator.
  2. In the target list, select the target that builds your application.
  3. Select the Build Settings tab.
  4. Scroll to Linking and open.
  5. Go to Other Linker Flags and double-click to open the popup.
  6. If the -ObjC flag is not in your list, click + and add it.
Warning: The -ObjC flag is necessary because the iOS Agent defines categories with methods that can be called at runtime, and by default, these methods are not loaded by the linker. As a result, you'll get an "unrecognized selector" runtime exception. The use of -ObjC ensures the methods will be loaded.