Visual Basic 1002005 [A Developers Notebook] [Electronic resources] نسخه متنی

1.4. Diagnose and Correct Errorson the Fly

Visual Studio does a great
job of catching exceptions, but it's not always as
helpful at resolving them. The new Exception
Assistant that's hardwired into Visual
Studio 2005 gives you a head start.

Note: Stumbled into a head-scratching exception? Visual Studio
2005 gives you a head start for resolving common issues with its
Exception Assistant.

1.4.1. How do I do that?

You don't need to take any steps to activate the
Exception Assistant. Instead, it springs into action as soon as your
program encounters an unhandled exception.

To see it in action, you need to create some faulty code. A good test
is to add the following event handler to any form, which tries to
open a non-existent file:

Private Sub Form1_Load(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles MyBase.Load
Dim XMLText As String = My.Computer.FileSystem.ReadAllText( _
"c:\FileDoesNotExist")
End Sub

Now run the application. When the error occurs, Visual Studio
switches into break mode and highlights the offending statement. The
Exception Assistant then appears, with a list of possible causes for
the problem. Each suggestion appears as a separate link in the pop-up
window. If you click one of these links, the full MSDN help topic
will appear. Figure 1-7 shows the result with the
faulty file-reading code; the Exception Assistant correctly
identifies the reason that the attempt to open the file failed.

Figure 1-7. Getting help with an exception

Note: This example uses a new VB language featurethe My
object. You'll learn much more about My objects in
the next chapter.

If you want to see the low-level exception information, click the
View Detail link at the bottom of the window. This pops up a dialog
box with a PropertyGrid showing all the
information of the associated exception object. This change alone is
a great step forward from Visual Studio .NET 2003, where you needed
to write a Catch exception handler and set a
breakpoint to take a look at the underlying exception object.

1.4.2. What about...

...solving complex problems? The Exception Assistant
isn't designed to help you sort through issues of
any complexity. Instead, it works best at identifying the
all-too-common "gotchas," such as
trying to use a null reference (usually a result of forgetting to use
the New keyword) and failing to convert a data
type (often a result of an inadvertent type cast).

1.4.3. Where can I learn more?

For help in the real world, consult a
colleague or one of the many .NET discussion groups. Some good
choices include http://lab.msdn.microsoft.com/vs2005/community
(for the latest on Visual Basic 2005) andonce Visual Basic
2005 enters its release phasehttp://www.windowsforms.net/Forums (for
Windows Forms questions), http://www.asp.net/Forums (for ASP.NET
issues), and http://discuss.develop.com/advanced-dotnetl
(for more advanced .NET queries).