reference the checkbox when you are using the checkbox set selector

i am using the checkbox set selector to be able to select a row from a grid.  But i am having difficulty to understand how i could refer to the check box. i mean how can i know if any of the row is selected? or how do i calculate that?
1 answers

When, where, why & how do you want to refer to the checkbox?

The checkbox selector is dealing/setting the association between two entities.
Thus the set value can be found in the owning entity/Association

Also: please checkout this learning path:
A lot of your questions will be answered there