Question

I have two dropdownlists, if one of them contain a value (not default value, which is empty string), the other should also have a value (like requredvalidator). But if no one has a value the page should validate ‘true’.
I cannot solve it with a validation group, because the button that trigger the validation is already triggering other validations.

Answer 1

Could you just use a custom validator control and put your logic in the server side validation method. Keep it in the same validation group.

<asp:CustomValidator ID="valCust" runat="server" 
                ControlToValidate="ddlControl" ErrorMessage="error Message" 
                ValidationGroup="Group" 
                onservervalidate="valCust_ServerValidate" >*</asp:CustomValidator>

code behind

 protected void valCust_ServerValidate(object source, ServerValidateEventArgs args)
{
     args.IsValid = MethodToWorkOutValidation();

}