Home > Articles > Programming > ASP .NET

This chapter is from the book

Server Controls

An important innovation in ASP.NET is server controls. They provide an event model that is startlingly similar to Windows GUI programming, and they encapsulate browser dependencies. They integrate seamlessly into the Visual Studio development environment. The end result is an extremely powerful tool for Web development.

We have been using server controls from the very beginning of the chapter, where we presented our "Hello" program. In this section we will look at server controls more systematically, and we will see a number of examples of interesting controls.

Web Controls

The most important kind of control in ASP.NET is the Web Forms server control or just Web control. These are new controls provided by the .NET Framework, with special tags such as <asp:textbox>. These controls run at the server, and they generate HTML code that is sent back to the browser. They are easy to work with, because they behave consistently. For example, you can determine the value returned by a control by using simple property notation.

Dim name As String = txtName.Text 

All of our previous examples of server controls in this chapter have been Web controls. In this section, we will look at several additional kinds of Web controls, including validation controls, list controls, and rich controls such as the Calendar control. But first we will look at HTML server controls.

HTML Server Controls

HTML server controls provide equivalent functionality to standard HTML controls, except that they run on the server, not on the client. In fact, the only way to distinguish an HTML server control from an ordinary HTML control on a Web page is the presence of the runat="server" attribute.

Here are two controls. Both are INPUT controls. The first is a server control. The second is of type password and is a regular HTML control.

<INPUT id=txtUserId
style="WIDTH: 135px; HEIGHT: 22px" type=text size=17
<INPUT id=""
style="WIDTH: 138px; HEIGHT: 22px" type=password size=17 

Working with HTML server controls is much like working with the Web Forms server controls we've used already. In server-side code you access the control through a control variable that has the same name as the id attribute. However, we are dealing with HTML controls, so there are some differences. You access the string value of the control not through the Text property but through the Value property. Here is some code that uses the value entered by the user for the txtUserId control.

lblMessage.Text = "Welcome, " & txtUserId.Value 

The advantage of HTML server controls for the experienced Web programmer is that they match ordinary HTML controls exactly, so that your knowledge of the details of HTML control properties and behavior carries over to the ASP.NET world. However, this similarity means they carry over all the quirks and inconsistencies of HTML. For example, rather than having two different controls for the somewhat different behaviors of a textbox and a password control, HTML uses in both cases the INPUT control, distinguishing between the two by the type=password attribute. Web Forms controls, in contrast, are a fresh design and have an internal consistency. Also, as we shall soon see, there is a much greater variety to Web Forms controls.


Let's look at an example of HTML controls. All of our server control examples in this section can be accessed from the page ServerCon-trols\WebForms1.aspx. (As usual, you should use IIS to configure the folder ServerControls as an application.) The top-level page gives you a choice of three examples,

  • HTML Controls
  • Validation
  • Calendar

Follow the link to HTML Controls, and you will come to a login page, as illustrated in Figure 14-34.

Figure 14-34Figure 14-34 Alogin page illustrating HTML server controls.

There is a textbox for entering a user ID and a password control for entering a password. Both of these controls are HTML INPUT controls, as shown previously. The textbox runs at the server, and the password is an ordinary HTML control. Clicking the Login button (implemented as a Windows Forms Button control) results in very simple action. There is one legal password, hardcoded at "77." The button event handler checks for this password. If legal, it displays a welcome message; otherwise, an error message.

Private Sub btnLogin_Click(ByVal sender As Object, _
  ByVal e As EventArgs) Handles btnLogin.Click
       If Request.Params("txtPassword") = "77" Then
           lblMessage.Text = "Welcome, " & txtUserId.Value
           lblMessage.Text = "Illegal password"
       End If 
End Sub 

Since the password control is not a server control, no server control variable is available for accessing the value. Instead, we must rely on a more fundamental technique, such as using the Params collection.10


It is easy to work with HTML controls in Visual Studio.11 The Toolbox has a palette of HTML controls, which you can access through the HTML tab. Figure 14–35 shows some of the HTML controls in the Visual Studio Toolbox.

Figure 14-35Figure 14-35 HTML controls in the Visual Studio Toolbox.

You can drag HTML controls onto a form, just as we have done with Web Forms controls. You have the option of using FlowLayout or GridLayout. The default is GridLayout, which enables absolute positioning of controls on a form. FlowLayout is the simplest layout, resulting in elements positioned in a linear fashion. You can set the layout mode through the pageLayout property of the form. In our example we used FlowLayout for the two INPUT controls and their associated labels.

The default choice for HTML controls is not to run at the server. To make an HTML control into a server control, right-click on it in the Form Designer. Clicking on Run As Server Control toggles back and forth between running on the server and not running on the server. You can inspect the runat property in the Properties panel, but you cannot change it there.

Validation Controls

The rest of our discussion of server controls will focus on Web controls. A very convenient category of control is the group of validation controls. The basic idea of a validation control is very simple. You associate a validation control with a server control whose input you want to validate. Various kinds of validations can be performed by different kinds of validation controls. The validation control can display an error message if the validation is not passed. Alternatively, you can check the IsValid property of the validation control. If one of the standard validation controls does not do the job for you, you can implement a custom validation control. The following validation controls are available:

  • RequiredFieldValidator
  • RangeValidator
  • CompareValidator
  • RegularExpressionValidator
  • CustomValidator

There is also a ValidationSummaryControl that can give a summary of all the validation results in one place.

An interesting feature of validation controls is that they can run on either the client or the server, depending on the capabilities of the browser. With an upscale browser such as Internet Explorer, ASP.NET will emit HTML code containing JavaScript to do validation on the client.12 If the browser does not support client-side validation, the validation will be done only on the server.


A very simple and useful kind of validation is to check that the user has entered information in required fields. Our second server control demonstration page provides an illustration. Back on the top-level ServerCon-trols\WebForms1.aspx page, follow the link to "Validation" (or click the Register button from the Login page). You will be brought to the page Regis-terNewUser.aspx, as illustrated in Figure 14–36. The screenshot shows the result of clicking the Register button after entering a UserId, a Password, and a First Name, but leaving Last Name blank. You will see an error message displayed next to the Last Name textbox, because that is where the validator control is on the form.

Figure 14-36Figure 14-36 Register New User page illustrates ASP.NET validation controls.

The textboxes for First Name and Last Name both have an associated RequiredFieldValidator control. In Visual Studio you can simply drag the control to a position next to the associated control. You have to set two properties of the validator control:

  • ControlToValidate must be set to the ID of the control that is to be validated.

  • ErrorMessage must be specified.

Then, when you try to submit the form, the validator control will check whether information has been entered in its associated control. If there is no data in the control, the designated error message will be displayed.

Internet Explorer supports client-side validation using JavaScript. You can verify that ASP.NET generates suitable JavaScript by looking at the generated source code in the browser (View | Source).

This form also requires that the UserId field not be blank. Since the primary validation of this field is done by a regular expression validator, as discussed shortly, we will use another technique for the required field validation. Figure 14–37 shows the location of the various validator controls in the Visual Studio Form Designer.

Figure 14-37Figure 14-37 Layout of validation controls for Register New User page.

We assign the ID vldUserId to the required field validator control associated with the UserId control, and we clear the error message. We also set the EnableClientScript property to False, to force a postback to the server for the validation. The event handler for the Register button then checks the IsValid property of vldUserId.

private void cmdRegister_Click(object sender,
                                                     System.EventArgs e)
     if (vldUserId.IsValid)
         lblMessage.Text = "Welcome, " + txtFirstName.Text;
         lblMessage.Text = "UserId must not be blank"; 

If the control is valid, we display the welcome message; otherwise, an error message. Note that we won't even reach this handler if other validation is false.


The RegularExpressionValidator control provides a very flexible mechanism for validating string input. It checks whether the string is a legal match against a designated regular expression. Our example illustrates performing a regular expression validation of UserId. The requirement is that the ID consist only of letters and digits, which can be specified by the regular expression

[ A-Za-z0-9]+

The following properties should normally be assigned for a RegularExpressionValidator control:

  • ValidationExpression (the regular expression, not surrounded by quotes)

  • ControlToValidate

  • ErrorMessage

You can try this validation out on our Register New User page by entering a string for UserId that contains a non-alphanumeric character.

Rich Controls

Another category of Web Forms controls consists of "rich controls," which can have quite elaborate functionality. The Calendar control provides an easy-to-use mechanism for entering dates on a Web page. Our third sample server control page provides an illustration, as shown in Figure 14–38.

The user can select a date on the Calendar control. The SelectedDate property then contains the selected date as an instance of the DateTime structure. You can work with this date by handling the SelectionChanged event. In our example page, the event handler displays the date as a string in a textbox.

Figure 14-38Figure 14-38 Using the Calendar control to select a date.

Private Sub Calendar1_SelectionChanged( _
  ByVal sender As Object, ByVal e As EventArgs) _
  Handles Calendar1.SelectionChanged
       txtDate.Text = _
End Sub 

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020