I seem to be having a massive problem with paths when browsing the SDK sources. Basically my issue is this:
I can import (for example) android.annotation.NonNull into my own project and it recognises the class fine. But if I open Activity.java I get random classes not being able to be found - but they exist in the correct path. For example it can find android.os.PersistableBundle (which exists at androidSDK\sources\android-23\android\os\PersistableBundle.java), but not android.annotation.NonNull (which exists at androidSDK\sources\android-23\android\annotation\NonNull.java)
I have tried invalidating caches and restarting, re-installing android studio, installing different versions and even redownloading the whole SDK, but nothing is making it happy. Is there a place I should be setting the 'root' path? How come it finds some classes but not others?