Including one Xcode project in another — linker errors

Question

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

Answer 1

Undefined symbols is a linker error

1.Check if you have added a library or framework

Project editor -> select a target -> General -> Linked Frameworks and Libraries
//or
Project editor -> select a target -> Build Phases -> Link Binary With Libraries

2.If you try to use Swift code from Objective-C

Add empty .swift file to the Objective-C project. When Xcode ask press Create Bridging Header