RequiredFieldValidator不触发

Question

I have a simple form with a required Validator on a textbox. When I leave the textbox blank and check the Page.isValid it is always true. I cannot figure out what I am doing wrong to cause the page to always be true.

<asp:TextBox ID="txtVendorTracking" runat="server" Width="150px"></asp:TextBox>
<asp:RequiredFieldValidator ID="rfvTxtVendorTracking" 
    InitialValue="Enter Vendor Tracking Nbr" runat="server" 
    ErrorMessage="Vendor Tracking Required." ControlToValidate="txtVendorTracking" 
    ValidationGroup="val" Display="Dynamic">*</asp:RequiredFieldValidator> 

    <asp:Button ID="btnSave" runat="server" Text="Save" Width="100px"  onclick="btnSave_Click" ValidationGroup="val"/>

           protected void btnSave_Click(object sender, EventArgs e)
        {
            Page.Validate(MasterValidation.ValidationGroup);
            if (!Page.IsValid)
            {
                ModalPopupExtender3.Show();
                txtRONbr.Focus();
                return;
            }
          }

Answer 1

Since initial state of the text box is empty, the problem is here:

InitialValue="Enter Vendor Tracking Nbr"

Per MSDN :

Validation fails only if the value of the associated input control matches this InitialValue upon losing focus.

Since the initial value of the validator is not an empty string, it treats an empty string as a valid input. TO solve thins you need to decide what whould be an initial state of your text box, and set up validator accordingly. For instance right now you should just remove InitialValue from the markup - it defauls to String.Empty .