Home > Articles

  • Print
  • + Share This
This chapter is from the book

Debugging ASP.NET Applications

The large number of ASP.old programmers migrating their code to ASP.NET ensures that error messages are one of the first things an ASP.NET programmer will typically see. Fortunately, not only is the debugging information provided by ASP.NET much better than ASP.old, but you have much more granular control over how debugging information is displayed in ASP.NET.

An ASP.NET debug page is displayed when an unhandled error is encountered, as long as the appropriate @Page or Web.config settings exist. The output of the page is composed of:

  • The application (or Web directory) where the error took place

  • The type of error and a description of the error

  • Details of the error from the compiler

  • Source code displaying where the error took place in your code

  • The file in which the error took place

  • Links to detailed compiler output and complete source code

  • Version information for the .NET runtime and ASP.NET

This rich debugging information isn't turned on by default, however. To access rich debugging information, you must turn debugging on, either at the page level (using an attribute of the @Page directive) or for the entire application (using a setting in Web.config).

Enabling Debugging at the Page Level

You can enable debugging at the page level by using an @Page directive.

<@ Page language="C#" debug="True" %>

Don't try testing this by creating an incorrectly coded ASP.NET page and trying to load it on localhost. Errors on the local machine always create debug information. The debug settings control what users on remote machines see. To test debug settings, you'll need to access your error page on a machine other than the Web server machine.

In case you haven't created one of your own already, Listing 3.4 contains an ASP.NET page that contains a bona fide error. You can use this page to test the way ASP.NET generates debug output code.

Listing 3.4 The First Mistake That Most ASP.NET Programmers Generally Make

<% @Page language="C#" debug="false" %>
<HTML>
 <HEAD>
  <TITLE>ASP.NET Error Page</TITLE>
  <SCRIPT runat='server'>
   public void Page_Load(Object Sender, EventArgs e)
   {
    Response.Write "This code will not work."
   }
  </SCRIPT>
 </HEAD>
 <BODY>
  This is my page. There are many others like it, but this one is mine.
 </BODY>
</HTML>

Note that this page has its Debug mode set to false. When you first load it (from a remote machine, remember), you'll get a message indicating that something is wrong with the code on the page. But the output won't display any additional information about the error; in particular, the source code display is suppressed. This is an extremely helpful security feature that ensures that your source code won't be displayed in an error condition unless you specifically permit it through an @Page attribute setting or a debug setting in Web.config.

Enabling Debugging at the Application Level

Turning debugging on and off at the page level is easy enough when you're making changes to only a few pages. But early in the development process, when nothing works, you may want to be able to turn Debug mode on for every page in your application.

You can turn debugging on for all the pages in a given folder by changing a setting in the Web.config file in that folder. You can activate Debug mode at the application level by setting the Debug attribute of the compilation section in Web.config.

Listing 3.5 shows an example of a Web.config file that activates debugging for an entire application.

Listing 3.5 A Web.config File That Activates Debugging at the Application Level

<configuration>
  <system.web>
   <customErrors mode="Off" />
   <compilation defaultLanguage="C#"
     debug="true"
     numRecompilesBeforeAppRestart="15">
   </compilation>
  </system.web>
</configuration>

That's it. Remember that when you test this option, it's meaningful only when you're debugging the application from a remote machine. Debug mode is always on when you're logging in to the Web application from localhost.

Using the Debug Object

The .NET framework provides a Debug object that you can use to assist with debugging your application. The Debug object is a member of System.Diagnostics.Debug. An instance of this object is created for you automatically, so you shouldn't ever need to instantiate it yourself. If you used the Debug object in Visual Basic, the .NET framework Debug object should be familiar to you.

Note

A complete reference to the properties and methods of the Debug object appears at the reference section at the end of this chapter.

The Write method is the most common member of Debug you'll use in your day-to-day programming. By using Debug.Write, you can send information to the development environment you run your ASP.NET application in. If you're using Visual Studio, the strings you send to Debug.Write are displayed in the Output window. (You can view them by running your Web application and then selecting View, Other Windows, Output, or by using the keyboard shortcut Ctrl+Alt+O.)

Listing 3.6 shows a typical call to Debug.Write, used to indicate that an ASP.NET page has loaded and its Page_Load event procedure has been entered.

Listing 3.6 Placing a Call to Debug.Write to Display Debug Information in the Development Environment

private void Page_Load(Object Sender , EventArgs e)
{
 Debug.Write("Application initializing. Poot.");
}

If you're not using Visual Studio or another integrated development environment to run and debug your ASP.NET application, calls to Debug.Write will go nowhere. A development environment must be present for the output generated by Debug.Write to be meaningful; if you need to send real-time debug information while your application is running, consider using Trace.Write (described earlier in this chapter) or a custom performance monitor (described in the next section).

  • + Share This
  • 🔖 Save To Your Account

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.

Overview


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.

Surveys

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.

Newsletters

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.

Security


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

Children


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

Marketing


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.

Choice/Opt-out


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.

Links


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