Page 114 - DCAP312_WEB_TECHNOLOGIES_II

Web Technologies-II

Notes Introduction

One of the main characters of ASP.NET over ASP is its new error handling features. The only
way to imprison errors in the ASP/VBScript was using the "On Error Resume Next" declaration
and scrutiny each line for an error with "If Err. Number <> 0 Then “statements. Developers who
were using JScript instead of the VBScript at the server-side where lucky. They have had access
to the "Try. Catch" statements provided by JScript. Well it is all over now. Now all the .NET
enabled languages support better error handling statements including VB.NET. Now, VB.NET
supports the "Try...Catch" statement. On top of this ASP.NET configuration file also supports
ASP.NET level error handling.
We always to create a problem-free function, one that always behaves as expected. In reality,
many things can go wrong while a program is running. As an application developer, you can
anticipate as much bad behaviour as possible so you can take appropriate actions. To assist
you with dealing with errors, the Visual Basic language provides many keywords, operators,
and techniques.

6.1 Logics of Error Handling

When an unhandled immunity propagates, the user may well be redirect to an error sheet using
different ASP.NET constitution settings. However, such a redirection may be prohibited in the
first place by treatment the exceptions that get thrown. Error handling in ASP.NET therefore,
may be divided into two separate logics:
• Redirecting the user to an error page when errors go unhandled.

• Handling exceptions when they get thrown.
6.1.1 Redirecting the User to an Error Page

There are two different scopes where we could specify which page the user has to be redirected
to, when errors go unhandled:

• Page level (applies to errors that happen within a single page).
• Application level (applies to errors that happen anywhere in the application).
Page Level
Use the error Page attribute in the web form.

This attribute defines the page the user should be redirected to when an unhandled exception
occurs in that specific.

The error Page attributes maps to the Page. Error Page property, and hence may be set
programmatically. The value may optionally include query string parameters. If no parameters
are added, ASP.NET would automatically add one with the name aspx error path. This parameter
would hold the value of the relative URL to this page, so that the error page would be able to
determine which page caused the error.
If a value is specified in this attribute (or property) and an unhandled exception occurs in the
page, the Page class would automatically perform a redirect to the specified page. If a value is
not specified, the exception is assumed to be unhandled, wrapped in a new Http Unhandled
Exception and then thrown, propagating it to the next higher level.
Application Level

Use the custom Errors section in web.config.

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