Hi Babai,
To achieve this, create an event in your view implementation class. lets say name is "EH_DROPDOWNVALUE".
Go to the get_p method of your attribute. write the code as below.
Now, when ever you will change the value of the drop down it will trigger your newly created event.
Inside the event you can refer your context node and get the attribute value.
lv_entity ?= me->typed_context->your context name->get_current()
lv_entity->get attribute( you attribute name).
Regards,
Jotsaroop Singh