Modifiy a variable in c++ program with the android UI in openframewroks?

Modifiy a variable in c++ program with the android UI in openframewroks?

I'm develloping an application with openframeworks, for android. I wish to
use the android UI for navigate into my app. But i block at the point how
to communicate my interaction with the android ui to my openframeworks'
code . I read a lot about JNI, but as far i understand it's allow to use
c++ code into java, but i don't find how to make it interact with the rest
of my code. When i write my jni/c++ function, i need to call it into that
:
extern "C" {
...
}
But i'm unable to modify any variable of my openframeworks program. How
can i do for by example get a boolean or a int from the android UI into
openframeworks ? Maybe i ask something impossible or i miss a point.
Regards