class YourAdapter extends StatelessWidget {

final Function onItemTap;

YourAdapter(
   {
    this.onItemTap
   });
    //do something like this on the onPressed of your item
    IconButton(
          icon: Icon(icon),
          color: Colors.deepPurpleAccent,
          onPressed: () {
            //this is the method that you passed as the reference in the
              constructor. It will call the original function.
            onItemTap(x,y);
          },
        )
}