On button click i want to show dropdown inside gridview, populated with some items (C#)

Question

Hello,

I want my dropdownlist which is inside the gridview should be populated with items on Button Click and rest fields of gridview should be blank untill on selectchange index of that dropdownlist.That is when i select id from dropdownlist 

it will show record related to that id in front in other fields of that gridview  ... some thing like this

And then automatically a new row is added to gridview..

and procedure repeats.

Please Help me i am not able to find any option for it.

Can anyone explain me hoe to achieve this issue.

Thanx 

Prerna