RequiredFieldValidator in ASP.NET

In this article I will explain what RequiredFieldValidator in ASP.NET is and what are the syntax and properties.

The RequiredFieldValidator control is used to make an input control a required field. This Validator control is ASP.NET control

The RequiredFieldValidator is actually very simple, and yet very useful. You can use it to make sure that the user has entered something in a TextBox control. Let's give it a try, and add a RequiredFieldValidator to our page. We will also add a TextBox to validate, as well as a button to submit the form with.

When you use the RequiredFieldValidator control inside an UpdatePanel control, make sure that the validator control and the control it is associated with are in the same panel.

Syntax:

<asp:RequiredFieldValidator />

 Main Properties:

o   ControlToValidate: Gets or sets the input control to validate.

o   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.

o   ErrorMessage: Gets or sets the text for the error message displayed in a ValidationSummary control when validation fails.

o   Text: Gets or sets the text displayed in the validation control when validation fails.

o   ValidationGroup: Gets or sets the name of the validation group to which this validation control belongs.

o   InitialValue: Specifies the starting value of the input control. Default value is ""

o   Runat: Specifies that the control is a server control. Must be set to "server"

Example 1: Below example is for DropDownList

<asp:DropDownList ID='ddlCompTypeFT' runat="Server" Width="150px" AutoPostBack="true" >  </asp:DropDownList>

                                    <asp:RequiredFieldValidator ID="rfvCompTypeFT" runat="server" InitialValue="0"

                                        Display="Dynamic" ForeColor="Red" ControlToValidate="ddlCompTypeFT" ValidationGroup="Add">*</asp:RequiredFieldValidator>

  Example 2: Below example is for TextBox

 <asp:TextBox ID='txtCoefficientET' runat="Server" Text='<%# Eval("Coefficient")%>'></asp:TextBox>

                                    <asp:RequiredFieldValidator ID="RFVCoefficientET" runat="server"

                                        Display="Dynamic" ForeColor="Red" ControlToValidate="txtCoefficientET" ValidationGroup="UPDATE">*</asp:RequiredFieldValidator>