Q:

Android Roboguice what is the purpose of extending a Robo Class? 

i am new to roboguice
i have been looking at their documentations i get the idea
yes, instead of saying 
 findViewById, i can just do @InjectView, etc

but what is the purpose of extending their classes, such as RoboAcitivy, or RoboFragment etc etc?  i mean what is the benefit of that?   I still don't see it. 
please helo

A:

I highly recommend you to look at RoboActivity class.  Then, I think, it would be clear for you. 
Roboguice is using annotations to know what and where to inject instances.  This is done in Injector which must be invoked somewhere.  Roboguice creators decided to run it in Activity.onCreate() method.  Therefore Activity is extended to RoboActivty which adds to onCreate() code such this below:
final RoboInjector injector = RoboGuice.getInjector(this);    
injector.injectMembersWithoutViews(this);

Injector will detect annotated fields and inject instances.