ASP.NET RequiredFieldValidator Control

The RequiredFieldValidator control is used to make an input control a required field.

With this control, the validation fails if the input value does not change from its initial value. By default, the initial value is an empty string ("").

Note: Leading and trailing spaces of the input value are removed before validation.

Note: The InitialValue property does not set the default value for the input control. It indicates the value that you do not want the user to enter in the input control.


Property Description
BackColor The background color of the RequiredFieldValidator control
ControlToValidate The id of the control to validate
Display The display behavior for the validation control. Legal values are:
  • None (the control is not displayed. Used to show the error message only in the ValidationSummary control)
  • Static (the control displays an error message if validation fails. Space is reserved on the page for the message even if the input passes validation.
  • Dynamic (the control displays an error message if validation fails. Space is not reserved on the page for the message if the input passes validation
EnableClientScript A Boolean value that specifies whether client-side validation is enabled or not
Enabled A Boolean value that specifies whether the validation control is enabled or not
ErrorMessage The text to display in the ValidationSummary control when validation fails.
Note: This text will also be displayed in the validation control if the Text property is not set
ForeColor The foreground color of the control
id A unique id for the control
InitialValue Specifies the starting value of the input control. Default value is ""
IsValid A Boolean value that indicates whether the control specified by ControlToValidate is determined to be valid
runat Specifies that the control is a server control. Must be set to "server"
Text The message to display when validation fails

Example of RequiredFieldValidator Control

Declare one TextBox controls, one Button control, and one RequiredFieldValidator control in an .aspx file. It shows how to use the RequiredFieldValidator control to make the "txt_name" textbox a required field.

C# code

using System;

namespace asptutorial
    public partial class blankpage : System.Web.UI.Page

        protected void Page_Load(object sender, EventArgs e)
            RequiredFieldValidator1.Text = "The name field is required!";
            RequiredFieldValidator1.ControlToValidate = TextBox2.ClientID;



	<form id="form1" runat="server">
		<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <br />
        <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
        <br />
        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" 
            ControlToValidate="TextBox1" ErrorMessage="The name field is required!"></asp:RequiredFieldValidator>


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