Validation ASP.Net Tutorial

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  4. RequiredFieldValidator requires a user to enter a value into a form field before submitting the form
Two important properties when  using the RequiredFieldValdiator control:
ControlToValidate: The ID of the form field being validated.
Text:              The error message.
<%@ Page Language="C#" %>
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">


    Show RequiredFieldValidator


    
    

            id="lblFirstName"
        Text="First Name:"
        AssociatedControlID="txtFirstName"
        Runat="server" />
            id="txtFirstName"
        Runat="server" />
            id="reqFirstName"
        ControlToValidate="txtFirstName"
        Text="(Required)"
        Runat="server" />
            id="lblLastName"
        Text="Last Name:"
        AssociatedControlID="txtLastName"
        Runat="server" />
    
            id="txtLastName"
        Runat="server" />
            id="reqLastName"
        ControlToValidate="txtLastName"
        Text="(Required)"
        Runat="server" />
            id="btnSubmit"
        Text="Submit"
        Runat="server" />