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RequiredFieldValidator
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If you ve ever registered for anything online, chances are that you ran into some kind of validator that checked to see if you had entered certain fields The ASPNET RequiredFieldValidator makes sure that the user fills in everything before the information is sent to a database table For each field you want completed by a user, you can use a RequiredFieldValidator that includes the name of the control to validate and an error message using the following format:
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ControlToValidate= "ControlName" ErrorMessage="Error message informing user that the field needs to be completed"
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Importantly, any form that must be completed can be named as the control to be validated So in addition to a TextBox control, others such as check boxes, radio buttons, and lists requiring selection can be validated as well
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Before going though the process of creating an example using a required field validation control, first see what your Design view looks like when you develop in Visual Studio 2008 Figure 9-1 shows what you see once you have completed the ASPNET portion of the application The messages Please enter your name and Please select your gender: are both error messages that only appear if the user leaves a required field blank However, when developing your application that uses a required field, the ability to see the error messages and their placement greatly aids in the design process If you prefer coding, you can use the Split mode and see the error message content and placement in the graphic portion of the Split window
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Design view shows all error messages and their placement
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Try This
Creating a Page with Required Validation
To see how to use the RequiredFieldValidator, this first validation example shows how to validate TextBox and RadioButtonList controls Keep in mind that while validation is important, equally important is that fields that do not require validation should not automatically require it and use up processing time With five fields Name, City, State, Zip, and Gender only two will be subject to validation, Name and Gender If any of the other fields is left blank, nothing happens Each of the two fields with
(continued)
ASPNET 35: A Beginner s Guide
validation has separate error messages so that if one is left unfilled, it is the only one that throws an error The following steps show how to create the application:
1 Open a new Web Site in Visual Basic 2008, and set the view to Design mode 2 Open the Validation menu in the Toolbox, and drag a RequiredFieldValidator control
onto the Design editor
3 Select the RequiredFieldValidator in the Design window and open the Properties
window Next to the ErrorMessage property, change the default message to Please enter your name
4 Add four TextBox controls and using Figure 9-1 as a guide, label and resize them 5 Select the RequiredFieldValidator and in the Properties window select
ControlToValidate under the Behavior directory In the pop-up menu, select TextBox1 (If you renamed your TextBox controls, select the one that will be used to accept entered names)
6 Drag a second RequiredFieldValidator control onto the Design editor, and change the
Error message to Please select your gender:
7 Drag a RadioButtonList to the Design window, and place it directly under the validator
you just placed
8 Select the required field validator, and in the Properties window choose
the ControlToValidate behavior; in the pop-up menu choose RadioButtonList1
9 Add a Button control and change the Text property value to Send Information 10 Double-click the Button to automatically generate an event handler 11 Finally add a Label control at the bottom and remove the Text property The following
shows the code for the ASPNET portion of the application:
ASPNET ReqFldaspx
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="ReqFldaspxcs" Inherits="_Default" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 10 Transitional//EN" "http://wwww3org/TR/xhtml1/DTD/xhtml1-transitionaldtd"> <html xmlns="http://wwww3org/1999/xhtml"> <head runat="server"> <style type="text/css"> div { font-family:Verdana; font-size:11pt;
9:
color:#0000cc; } </style> <title>Required Field Validation</title> </head> <body> <form id="form1" runat="server"> <div> Please fill out the form:<br /> *Required field:
Validation Controls
<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate= "TextBox1" ErrorMessage="Please enter your name" /><br /> <asp:TextBox ID="TextBox1" runat="server" />  *Name<br /> <asp:TextBox ID="TextBox2" runat="server" />  City<br /> <asp:TextBox ID="TextBox3" runat="server" Width="38px" />  State<br /> <asp:TextBox ID="TextBox4" runat="server" Width="72px" />  Zip<br /> <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate= "RadioButtonList1" ErrorMessage="Please select your gender:" /> <br /> *Gender <asp:RadioButtonList ID="RadioButtonList1" runat="server"> <asp:ListItem>Male</asp:ListItem> <asp:ListItem>Female</asp:ListItem> </asp:RadioButtonList> <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Send Information" /> <br /> <asp:Label ID="Label1" runat="server" /> <br /> </div> </form> </body> </html>
The C# portion of the application is very short All you need to do is to remove the default Page_Load function and add a single statement to the Button_Click event handler as shown in the following code listing: (continued)
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