how to validate data inside a ModalPopupExtender control?

[hanglam]

Hi,

I'm using a ModalPopupExtender with two buttons, an OK button and a Cancel button?

I want to link the OK button to both the onOKScript and onClick event.

In my ModalPopupExtender I have a bunch of DropDownList that I need the user to fill out before closing the ModalPopupExtender.
How do I validate the information from the user without closing the ModalPopupExtender and if the information is valid, how do I do a postback to the server to process the information selected by the user?

My idea was to use both the onOKScript to run some Javascript code and the onClick event to run server-side code.

but which one come first the onOKScript and then the onClick event ? or is it the other way around? and any idea on how to validate the DropDownList information in Javascript? I'm not very familiar with Javascript code.

I'm using ASP.NET 4.0 and the ModalPopupExtender Ajax control.

Thanks,
Hang