Retain values in dropdown,after closing the popup window

Hi, 

I have a web page(C#), which has a dropdown and a button., Clicking on the button invokes a child (popup) window.  In the child window, i have a button to close the child window(using javascript) and pass the values from the child window to the parent window.

closing the popup window, refreshes the parent window(i need to refresh the parent window) and clears the selected data in the dropdown to the default values in the parent window.

How to retain the selected values in the dropdown(available in the parent page) after closing the child window?

Thank you.
...