Application Error Handling Vb.net
resources Windows Server 2012 resources Programs MSDN subscriptions Overview Benefits Administrators Students Microsoft Imagine Microsoft Student Partners ISV Startups TechRewards Events Community Magazine Forums Blogs Channel 9 Documentation APIs and reference Dev centers Retired content Samples We’re sorry. The content you requested has been removed. You’ll be auto redirected in 1 second. Visual Basic Developer Visual Basic Developer 2001 June 2001 June 2001 Error Handling the VB.NET Way: Living with Exceptions Error Handling the VB.NET Way: Living with Exceptions Error Handling the VB.NET Way: Living with Exceptions Error Handling the VB.NET Way: Living with Exceptions TOC Collapse the table of content Expand the table of content This documentation is archived and is not being maintained. This documentation is archived and is not being maintained. Visual Studio 6.0 This article may contain URLs that were valid when originally published, but now link to sites or pages that no longer exist. To maintain the flow of the article, we've left these URLs in the text, but disabled the links. Error Handling the VB.NET Way: Living with Exceptions Gary Cornell and Jonathan Morrison In Debbie Cooper's article this month, she shows how to use API functions to retrieve error numbers and error messages in VB6. Here, Gary Cornell and Jonathan Morrison illustrate how VB.NET's new structured error handling is going to change how we code. This article is adapted from their forthcoming book, Programming VB.NET: A Guide for Experienced Programmers (Apress, ISBN 1893115992). Unfortunately, bad things can happen to good programs: A network connection might go down, the printer might run out of paper, and so forth. As the programmer, it's not your fault when these things happen, but it's not the user's fault when the network goes down, either. At the
resources Windows Server 2012 resources Programs MSDN subscriptions Overview Benefits Administrators Students Microsoft Imagine Microsoft Student Partners ISV Startups TechRewards Events Community Magazine Forums Blogs Channel 9 Documentation APIs and reference Dev centers Retired content Samples We’re sorry. The content you requested has been removed. You’ll be auto redirected in 1 second. MSDN Library MSDN Library MSDN Library MSDN Library Design Tools Development Tools and Languages Mobile and Embedded Development .NET Development Office development Online Services Open Specifications patterns & https://msdn.microsoft.com/en-us/library/aa227603(v=vs.60).aspx practices Servers and Enterprise Development Speech Technologies Web Development Windows Desktop App Development TOC Collapse the table of content Expand the table of content This documentation is archived and is not being maintained. This documentation is archived and is not being maintained. How to: Handle Application-Level Errors Other Versions Visual Studio 2010 .NET Framework 4 https://msdn.microsoft.com/en-us/library/24395wz3.aspx Visual Studio 2008 .NET Framework 3.0 Visual Studio 2005 This code example shows how to create an error handler in the Global.asax file that will catch all unhandled ASP.NET errors while processing a request — in other words, all the errors that are not caught with a Try/Catch block or in a page-level error handler. In the example, the handler transfers control to a generic error page named GenericErrorPage.aspx, which interprets the error and displays an appropriate message. Example The following example is from a complete code sample in Complete Example for Error Handlers. Security Note Never set customErrors to Off in your Web.config file if you do not have an Application_Error handler in your Global.asax file. Potentially compromising information about your Web site can be exposed to anyone who can cause an error to occur on your site. C#VB Copy void Application_Error(object sender, EventArgs e) { // Code that runs when an unhandled error occurs // Get the exception object. Exception exc = Se
VB.Net - Program Structure VB.Net - Basic Syntax VB.Net - Data Types VB.Net - Variables VB.Net - Constants VB.Net - Modifiers VB.Net - Statements VB.Net - Directives VB.Net - Operators VB.Net - Decision Making VB.Net - Loops VB.Net - Strings VB.Net - Date & Time VB.Net - Arrays VB.Net https://www.tutorialspoint.com/vb.net/vb.net_exception_handling.htm - Collections VB.Net - Functions VB.Net - Subs VB.Net - Classes & Objects VB.Net - Exception Handling VB.Net - File Handling VB.Net - Basic Controls VB.Net - Dialog Boxes VB.Net - Advanced Forms VB.Net - Event Handling VB.Net Advanced Tutorial VB.Net http://mikehadlow.blogspot.com/2009/08/first-rule-of-exception-handling-do-not.html - Regular Expressions VB.Net - Database Access VB.Net - Excel Sheet VB.Net - Send Email VB.Net - XML Processing VB.Net - Web Programming VB.Net Useful Resources VB.Net - Quick Guide VB.Net - Useful Resources VB.Net - Discussion Selected Reading Developer's Best application error Practices Questions and Answers Effective Resume Writing HR Interview Questions Computer Glossary Who is Who VB.Net - Exception Handling Advertisements Previous Page Next Page An exception is a problem that arises during the execution of a program. An exception is a response to an exceptional circumstance that arises while a program is running, such as an attempt to divide by zero. Exceptions provide a way to transfer control from one part of a program to another. VB.Net exception handling is built application error handling upon four keywords: Try, Catch, Finally and Throw. Try: A Try block identifies a block of code for which particular exceptions will be activated. It's followed by one or more Catch blocks. Catch: A program catches an exception with an exception handler at the place in a program where you want to handle the problem. The Catch keyword indicates the catching of an exception. Finally: The Finally block is used to execute a given set of statements, whether an exception is thrown or not thrown. For example, if you open a file, it must be closed whether an exception is raised or not. Throw: A program throws an exception when a problem shows up. This is done using a Throw keyword. Syntax Assuming a block will raise an exception, a method catches an exception using a combination of the Try and Catch keywords. A Try/Catch block is placed around the code that might generate an exception. Code within a Try/Catch block is referred to as protected code, and the syntax for using Try/Catch looks like the following: Try [ tryStatements ] [ Exit Try ] [ Catch [ exception [ As type ] ] [ When expression ] [ catchStatements ] [ Exit Try ] ] [ Catch ... ] [ Finally [ finallyStatements ] ] End Try You can list down multiple catch statements to catch different type of exceptions in case your try block raises more than one exception in different situatio
We would catch it and write it to a log. More sophisticated versions even featured a stack trace. Yes, really, we were that advanced :) The reason we did that was simple, VB didn't have structured exception handling and if your application threw an unhandled error it simply crashed. There was no default way of knowing where the exception had taken place. .NET has structured exception handling, but the VB mindset of wrapping every piece of code in a try-catch block, where the catch catches System.Exception, is still common, I see it again and again in enterprise development teams. Usually it includes some logging framework and looks something like this: try { // do something } catch (Exception exception) { Logger.LogException("Something bad just happened", exception); } Catching System.Exception is the worst possible exception handling strategy. What happens when the application continues executing? It's probably now in an inconsistent state that will cause extremely hard to debug problems in some unrelated place, or even worse, inconsistent corrupt data that will live on in the database for years to come. If you re-throw from the catch block the exception will get caught again in the calling method and you get a ton of log messages that don't really help you at all. It is much better to simply allow any exceptions to bubble up to the top of the stack and leave a clear message and stack trace in a log and, if possible, some indication that there's been a problem on a UI. In fact there are only three places where you should handle exceptions; at the process boundary, when you are sure you can improve the experience of the person debugging your application, and when your software can recover gracefully from an expected exception. You should always catch exceptions at the process boundary and log them. If the process has a UI, you should also inform the user that there has been an unexpected problem and end the current business process. If you allow the customer to struggle on you will most likely end up with either corrupt data, or a further, much harder to debug, problem further down the line. Improving the debugging experience is another good reason for exception handling. If you know something is likely to go wrong; a configuration error for example, it's worth catching a typed error (never System.Exception) and adding some context. You could explain clearly that a configuration section is missing or incorrect and give explicit instructions on how to fix it. Be very careful though, it is very easy to end up sen