title: Including one Xcode project in another -- linker errors
body: <p>I am trying to do this, and running into problems.  The parent project needs to access the class SettingsViewController from the child project.  I have put the child project path into my header search paths.  Everything compiles OK, but I get linker errors, as follows:</p>
  
  <blockquote>
    <p>Undefined symbols:   "_OBJC_METACLASS_$_SettingsViewController",
    referenced from:
          _OBJC_METACLASS_$_StatisticsViewController in StatisticsViewController.o   "_OBJC_CLASS_$_SettingsViewController",
    referenced from:
          objc-class-ref-to-SettingsViewController in SelectionViewController.o
          _OBJC_CLASS_$_StatisticsViewController in StatisticsViewController.o ld: symbol(s) not found collect2: ld
    returned 1 exit status</p>
  </blockquote>
  
  <p>How can I fix this?</p>