A simple use of the RequiredFieldValidator server control (C#) : RequiredFieldValidator « Validation « ASP.NET Tutorial

<%@ Page Language="C#" %>

<script runat="server">
    protected void Button1_Click(Object sender, EventArgs e) {
       Label1.Text = "Page is valid!";
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>RequiredFieldValidator</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:TextBox ID="TextBox1" Runat="server"></asp:TextBox>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" 
                                    Runat="server" 
                                    ErrorMessage="Required!" 
                                    ControlToValidate="TextBox1">
        </asp:RequiredFieldValidator>
        <asp:Button ID="Button1" 
         Runat="server" 
         Text="Submit" 
         OnClick="Button1_Click" />
        <asp:Label ID="Label1" Runat="server"></asp:Label>    
    </div>
    </form>
</body>
</html>

8.11.RequiredFieldValidator
	8.11.1.	RequiredFieldValidator requires a user to enter a value into a form field before submitting the form.
	8.11.2.	Use asp:RequiredFieldValidator to check the input of an asp:TextBox (VB.net)
	8.11.3.	Use the RequiredFieldValidator's InitialValue to set a default value
	8.11.4.	Specify ErrorMessage for asp:RequiredFieldValidator
	8.11.5.	asp:RequiredFieldValidator will be converted to JavaScript Code after loading in client side
	8.11.6.	A simple use of the RequiredFieldValidator server control (C#)
	8.11.7.	Text field of RequiredFieldValidator server control (VB)
	8.11.8.	Placing values between nodes
	8.11.9.	Working with the InitialValue property
	8.11.10.	Using two RequiredFieldValidator controls for one form element
	8.11.11.	Validating Drop-Down Lists with the RequiredFieldValidator Control
	8.11.12.	Using images for error notifications
	8.11.13.	Disabling client-side validations in a validation control
	8.11.14.	Using sound for error notifications
	8.11.15.	EnableClientScript=false, Display=Static
	8.11.16.	RequiredFieldValidator for login page
	8.11.17.	RequiredFieldValidator with server side validation
	8.11.18.	Hard code error message
	8.11.19.	RequiredFieldValidator Dynamic Display