This can't be that hard but I can't seem to find a way to do it... I have googled several different ideas to no avail. this is what I need to do.

I have an ASP.NET Page with a button - Of course the code behind is C#. When the user clicks the button I want check if there are any selected items (that is no problem) if there aren't any selected items I need to pop up and alert - that tells them this...

Can someone point me in the right direction on this? I would think it would be simple but I can't find anything that shows how to conditionally call a java alert - or some sort of alert...

Thanks!!!