RequiredFieldValidator for a dropdownlist

Question

I have a dropdownlist which I am developing dynamically in the code.

  Dim objPreferenceDropdownList As DropDownList = New DropDownList()
                        objPreferenceDropdownList.ID = "objPreferenceDropdownList"
                        objPreferenceDropdownList.AppendDataBoundItems = "True"

              objPreferenceDropdownList.AutoPostBack = True

I am populating this dropdown with different items such as

objPreferenceDropdownList.Items.Add(new ListItem("--Select Color--","0"));

 objPreferenceDropdownList.Items.Add(new ListItem("Red","1"));

 objPreferenceDropdownList.Items.Add(new ListItem("Blue","2"));

objPreferenceDropdownList.Items.Add(new ListItem("White", "3"));

objPreferenceDropdownList.Items.Add(new ListItem("Pink", "4"));

Now I need to validate the dropdownlist it there is no any item selected in the dropdown for that I created a required field validator dynamically like this:

Dim reqPrefGroupValidator As RequiredFieldValidator = New RequiredFieldValidator()
                                reqPrefGroupValidator.ControlToValidate = "objPreferenceDropdownList"
                                reqPrefGroupValidator.InitialValue = "0"
                                reqPrefGroupValidator.SetFocusOnError = True
                                prefdiv.Controls.Add(reqPrefGroupValidator)

The problem is required field validator only works when dropdownlist is empty what if I need to fire requiredfieldvalidator when the selected item value of dropdownlist is zero.

Answer 1

Set the InitialValue of the validator to 0 and the validator must have and ID ofcourse as:

<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" 
        ErrorMessage="RequiredFieldValidator" ControlToValidate="objPreferenceDropdownList" 
        InitialValue="0"></asp:RequiredFieldValidator>