how to add filter extension to a file upload in asp.net

Question

Possible Duplicate:
How do I Validate the File Type of a File Upload?

i would like to add file extension for filtering to file upload control in my asp.net page.and do validation on client side.

how can i set file extension dynamically..

ex:images only(.jpg;.png;*.gif;).

Answer 1

in Properties pane>Filter> "txt files (.txt)|.txt|All files (.)|."

or object.Filter("txt files (.txt)|.txt|All files (.)|.");