So to understand a bit better what functionality that you are trying to achieve.
To the best of my understanding, a type 3 form is used for MAINTAIN or DISPLAY of a main-table. So the view field has to be a part of the INDEX of the main table.
Assuming that the session was generated properly with a main-table behind it, the view field by default will accept values and display the first set of matching records (assuming that the start option is FIND-DATA).
So, if you can specify in bit more detail what functionality you are trying to achieve - you may not even need a type 3 form, all it needs to be could be a (Print Session) form, if you are using the entered field value to call some function.
You could attempt the after.input event of the field, that is just a vague suggestion without much understanding what you are trying to do.