Need to Know More?

The Visual Studio .NET Combined Help Collection, including Introduction to Web Forms State Management and Web Forms Page Processing .

Onion, Fritz. Essential ASP.NET . Reading, MA: Addison-Wesley, 2002.

Watch the Visual Studio .NET Seminars at www.msdn.com/seminar/mmcfeed/mmcdisplayfeed.asp?Lang=en&Product=103328&Audience=100402.

Read the How-To articles on Web Development at www.msdn.com/howto/webdev.asp#asp.

Visit ASP.NET Forums at www.asp.net/forums.

Download the ViewState Decoder utility from www.develop.com/devresources/resourcedetail.aspx?type=t&id=827.

Review the ASP.NET state management articles at http://support.microsoft.com/common/canned.aspx?Sz=kbstate.

Review the ASP.NET How-To articles at http://support.microsoft.com/common/canned.aspx?LL=kbaspnetSearch&Sz=kbhowtomaster.

Chapter 5. Error Handling for the User Interface

Terms you'll need to understand:

Application.Error event
Custom error pages
Custom exceptions
Exception
Page.Error event
The catch block
The finally block
The throw statement
The try block
Unhandled exceptions

Techniques you'll need to master:

Knowing how to handle exceptions using the try - catch - finally blocks
Knowing how to create custom exception classes and custom error messages; learn to implement them in a program
Knowing how to configure custom error pages in the web.config file
Experimenting with code that performs error handling at the Page_Error() or Application_Error() event handlers

Exception handling helps you in creating robust applications. Fortunately, exception handling is an integral part of the .NET Framework. The framework classes, as well as user-defined classes, throw exception objects to indicate unexpected problems in the code. In this chapter, you will learn how to handle exceptions in ASP.NET Web applications.

Understanding Exceptions

An exception occurs when a program encounters any unexpected problem, such as running out of memory or attempting to read from a file that no longer exists.

An exception generally results in abruptly terminating the program after displaying an error message. Ideally, your program should be capable of handling these exceptional situations and, if possible, gracefully recover from them. This is called exception handling . Proper use of exception handling can make your programs robust, as well as easy to develop and maintain.

The Common Language Runtime (CLR) views an exception as any object that encapsulates any information about the problems that occurred during program execution. The FCL provides two categories of exceptions:

ApplicationException ” Represents exceptions thrown by applications
SystemException ” Represents exceptions thrown by the CLR

Both of these exception classes derive from the base Exception class. Table 5.1 lists the important properties of all three of these classes.

Table 5.1. Important Properties of the Exception Class

Property	Description
HelpLink	Specifies the uniform resource locator (URL) of the help file associated with this exception.
InnerException	Specifies an exception associated with this exception. This property is helpful when a series of exceptions is involved. Each new exception can preserve the information about the previous exception by storing it in the InnerException property.
Message	Specifies textual information that indicates the reason for the error and provides possible resolutions .
Source	Specifies the name of the application causing the error.
StackTrace	Specifies where an error occurred. If the debugging information is available, the stack trace includes the name of the source file and the program line number.
TargetSite	Represents the method that throws the current exception.

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Need to Know More?

Need to Know More?

Chapter 5. Error Handling for the User Interface

Understanding Exceptions

Table 5.1. Important Properties of the Exception Class

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