Using Drop down box in a table control

Hi,

I'm new to ABAP. I'm trying to use drop down boxes as fields inside a table control.Im using 2 fields (f1 and f2). I want to dynamically populate values in f2 based on f1 i.e once i choose a value in f1 and click on f2 , it should give me a list of values in f2 based on the value of f1. f1 and f2 are from different tables.

what i have done : i am able to populate values in f2 (based on the value of f1)

Problem::

1. Once i choose a value in the field f1, the value is not remaining in the field. Once i choose, the value blinks for a while and goes off ! ... ( my guess :: PBO is clearing it )

2. After i choose a value in f1 in the first row, the corresponding values in f2 are getting populated in all the rows.