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This article mainly introduces how to use VB.NET structured exception handling, the article introduces in great detail, has a certain reference value, interested friends must read it!

Overview

Compared with VB language, VB.NET introduces many features. One of the most noteworthy changes is the introduction of VB.NET structured exception handling. Although VB.NET still supports exception handling of type On Error Goto, this is not very good. We should take full advantage of the structured exception handling provided by VB.NET.

Proper error handling is important

Any application needs an appropriate exception handling. However, due to strict development time constraints, shared responsibilities, and conflicting priorities, developers often overlook the importance of organized and thoughtful exception handling. This often leads to inconvenience and failure for users, and * has to add a lot of code rewriting work.

Structured exception handling

VB.NET uses the standard error reporting mechanism of the .NET Framework architecture, known as structured exception handling; it reports errors in medical programs based on exceptions. Exceptions are classes that can catch error messages. In order to properly use the exception handling mechanism of .NET, developers need to write clever code to closely observe exceptions, as well as write execution code to handle them.

VB.NET structured exception handling provides the following sections in the code:

Try snippet: a code snippet that can generate an exception and can always be executed

Catch snippet: a code snippet that attempts to handle an exception and is executed when the exception occurs

Finally snippet: a code snippet that does some cleanup and can always be executed

Abnormal class

Every exception class in .NET is derived from the System.Exception class. The most frequently used members of the exception class are as follows:

Message: describe the specific information of an error

Source: the name of the object or application that caused this exception

Goal: ways to handle exceptions

Try...Catch block

The purpose of the Try...Catch block is to allow errors to be caught and to specify a specific VB.NET structured exception handling solution for them. The code looks like this:

Try 'executed code Catch' error resolution code Catch ends

Use Try snippets to write the code to be executed, and Catch snippets to catch errors that may occur when executing Try snippets of code and react accordingly. The protection code that appears in the Try section is always executed; however, the code in the Catch section is executed only when an error occurs. The Try segment of the code is always executed.

Try...Catch...Finally block

The purpose of using the Try...Catch...Finally block is to allow the protected code in the Try section to be executed, to react to any possible errors in the Catch block, and to have cleanup code in the subsequent Finally block. The code in the Try block is executed regardless of whether there is an error in the Finally block. In this way, it is convenient to ensure that the allocated resources will be released, and it can easily provide functions that need to be performed regardless of the error control details. The code example is as follows:

Try 'execute Code Catch' error Resolution Code Finally 'Clean Code Catch end

Catch all exceptions and concrete classes of exceptions

VB.NET structured exception handling is flexible, allowing you to catch a specific type of exception or any type of exception, depending on how we use it.

Example: catch any possible exception

Try Dim i As Integer = 0 Dim iresult As Integer iresult = 1 / I

Using ex as an exception catch

MessageBox.Show

(ex.ToString ())

Finally

MessageBox.Show

("finally block executed")

End of Try

How does this work?

In the above VB.NET structured exception handling code example, we deliberately set a run error to prove that any exception can be caught. We catch any error that occurs and react to it, regardless of the type of error. The error occurs in the Try code block, so when the exception occurs, the Catch code block is then executed, followed by the Finally code block. We catch this exception by declaring a variable of exception type ex.

Example: catch a specific type of exception

Try Dim i As Integer = 0 Dim iresult As Integer iresult = 1 / I

Catch ex as an exception of the overflow type

MessageBox.Show

(ex.ToString ())

Finally

MessageBox.Show

("finally block executed")

End of Try

How does this work?

The second code example causes the same error because it attempts to perform a division by 0, which causes an overflow. However, in this example, we are only interested in catching exceptions of this type, so the type of ex variable is specifically defined as the OverflowException type. The code result of running the second example is the same as running the * example, because the same error is caught in both examples; however, the second example cannot catch other types of exceptions (exceptions of non-overflow types). But as before, the code in the Finally block is executed regardless of whether an exception is caught or not.

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