How to go about validating AJAX cascading drop down lists - asp.net

Question

I am using the AJAX Cascading drop down list but want to add event validation e.g. the compare validators.
As the cascading drop down list requires the page event validation to be disabled what is the best way to do the validation?
Thanks
Andy
Validation Attempt:
I have tried to use a custom validator which calls a Javascript function but it doesnt seem to be picking up the control. I get the following error Microsoft JScript runtime error: Object required
function ValidateCostCentCat(source, arguments)
{
var countryList = document.getElementById("ddlCategory");
if (null != countryList)
{
var iValue = countryList.options[countryList.selectedIndex].value;
if (iValue == "Select Category")
{
arguments.IsValid = true;
}
else
{
arguments.IsValid = false;
}
}
}
The mark-up for the custom validator is
<asp:CustomValidator ID="valcustCategory" runat="server" CssClass="error" Display="Dynamic" ValidationGroup="DirectHire" ClientValidationFunction="ValidateCostCentCat"
ErrorMessage="Please select a Cost Centre Category from the drop down list provided.">!</asp:CustomValidator>

Answer 1

Read This: http://www.w3schools.com/PHP/php_ajax_database.asp
The example demostrate how to select a
value from a dropdown box sent it via
AJAX and get back the responce!
in the middle you can do all the
Validation that you want!
UPDATED with code just for fun! ;-)
Assuming your select is
<asp:DropDownList ID="CategoryDropDownList" runat="server">
Then you function look like this:
function ValidateCostCentCat(source, arguments)
{
var countryList = document.getElementById("CategoryDropDownList");
if (null != countryList)
{
var iValue = countryList.options[countryList.selectedIndex].value;
if ( iValue == "Select Category" ) {
arguments.IsValid = true;
} else {
arguments.IsValid = false;
}
}
}
This must work as expected!
hope this help!