Just an example from the original article, but it is self explanatory
<asp:DropDownList ID="ddlMimeType" runat="server">
<asp:ListItem Value="mp3">audio/mpeg</asp:ListItem>
<asp:ListItem Value="wma">audio/wma</asp:ListItem>
<asp:ListItem Value="other">Other</asp:ListItem>
</asp:DropDownList>
<asp:TextBox id="txbOtherMimetype" runat="server" />
<asp:RequiredFieldValidator id="valOtherMimetypeRequired" runat="server"
ControlToValidate="txbOtherMimetype" ForeColor="#990066"
ErrorMessage="You have to specify a custom mimetype." />
<script type="text/javascript">
$(document).ready(function()
{
$("#<%= ddlMimeType.ClientID %>").change(function()
{
toggleOtherMimeType(this);
});
}
function toggleOtherMimeType(elem)
{
if(elem!=undefined)
{
if(elem.value=="other")
{
$("#<%= txbEnclosureOtherMimetype.ClientID %>").show();
ValidatorEnable($("#<%= valEncOtherMimetypeRequired.ClientID %>")[0], true);
}
else
{
$("#<%= txbEnclosureOtherMimetype.ClientID %>").hide();
ValidatorEnable($("#<%= valEncOtherMimetypeRequired.ClientID %>")[0], false);
}
}
}
</script>
