Hallo Bharathy,
I have implemented the event DDLB_CLICK within the implementation class.
Please see the attached file. 
But the situation is like to the previous post.
I show you why. Once I select the first entry the selection of the field Portfolioelement is fine.
Then I select the second line and I still get the same entries.
And so on whenever I select other lines:
I have a question related to the point 2:
2. By any chance, if you have "if rv_valuehelp_descriptor is bound" in field 2 GET_V method, remove/ handle it properly.
Reason: System may skip the ddlb fill logic, if the rv_valuehelp_descriptor instance is bound. In your case, the get_v should gets executed completely every time.
I do not understand totally your hint. Where am I supposed to correct the code?
In any case many thanks for your patience.
Best regards,
Andrea