Name

Try...Catch...Finally Statement

Synopsis

Try
   tryStatements
[Catch1 [exception [As type]] [When expression]
    catchStatements1
[Exit Try]

Catch2 [exception [As type]] [When expression]
    catchStatements2
[Exit Try]
...
Catchn [exception [As type]] [When expression]
    catchStatementsn]
[Exit Try]

[Finally
   finallyStatements]
End Try
exception optional; System.Exception or a derived type

The exception to catch. If exception is omitted or if it is System.Exception, all exceptions will be caught. However, if exception is omitted, no information about the exception will be accessible within the Catch block.

type optional

The data type of the exception to be handled by the Catch block. Its value can be System.Exception or any derived type. If omitted, its value defaults to System.Exception, and all exceptions will be handled.

expression optional; Boolean

A logical expression that defines a condition under which the error is to be handled by the Catch block.

Description

Handles runtime errors using Structured Exception Handling.

The tryStatements, which are required, constitute the Try block and are the statements that VB monitors for errors.

The Catchblocks, of which there can be more than one, contain code that is executed in response to VB “catching” a particular type of error within the Try block. Thus, the Catch blocks consist of the error-handlers for the Try block.

The phrases exception [As type] and [When expression] are referred to as filters in the VB.NET documentation. In the former case, exception is either a variable of type Exception, which is the base class that “catches” all exceptions, or a variable of one of Exception’s derived classes. The When filter is typically used with user-defined errors.

The Exit Try statement is used to break out of any portion of a Try...Catch...Finally block.

The optional finallyStatements code block is executed regardless of whether an error occurs (or is caught), unless an Exit Try statement is executed.

Multiple Catch statements can be used. However, only the first Catch statement to be true is executed. This means that multiple Catch statements should be ordered from most specific to most general, with a Catch block handling errors of type System.Exception occurring last.

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset