Custom Error Handler

[alex_read]

Can anyone tell me how I could get this working please??? I'm trying to create my own exception type which can be used in plase of the .Net framework one:

Public Class Form1 ...

    Private Sub Command1_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles cmdGenExcep_DivideBy0.Click
        Try
            throw new System.OverflowException 
        Catch Ex as Class1
            messagebox.Show(ex.message)
        End Try
    End Sub

End Class


Public Class Class1
    Inherits Exception

    Public sub new(ByRef strExcepMessage As String)
        mybase.New(strExcepMessage) 
    End Sub
End Class

[mendhak]

First, give it a better name than Class1

Public Class HairyException
    Inherits System.Exception

Private _mStrException As String

    Public sub new(ByRef strExcepMessage As String)
        _mStrException = strExcepMessage
    End Sub
End Class

Then to use it,

    Private Sub Command1_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles cmdGenExcep_DivideBy0.Click
        Try
            throw new HairyException("OMFG") 
        Catch Ex as HairyException
            messagebox.Show(ex.message)
        End Try
    End Sub

End Class

One thing I haven't done in the code yet is to create a message property. do this yourself, create a readonly property called message of type string, and use mStrException

[alex_read]

Nope, no good!

Did you try that one out/ did this work on your machine?

[mendhak]

Nope, haven't tried it.

[mendhak]

DId you override the Message property?

[alex_read]

Yep!

[mendhak]

So I finally opened up VS.NET.

Public Class HairyException
    Inherits System.Exception

    Private _msg As String


    Public Sub New(ByVal strMsg As String)
        _msg = strMsg

    End Sub


    Overrides ReadOnly Property Message() As String
        Get
            Return _msg

        End Get
    End Property

End Class

and in the form:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            Throw New HairyException("Holy cow!")

        Catch ex As HairyException

            MessageBox.Show(ex.Message)

        End Try


    End Sub

Worked for me. Try copy pasting.

[alex_read]

Ok, sorry, to expand on that then...

Yes this works fine, if I have a hairyexception thrown manually:

Public Class frmTesting_ExcepHndl 
    Inherits System.Windows.Forms.Form ...

    Private Sub cmdGenExcep_DivideBy0_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles cmdGenExcep_DivideBy0.Click
        Try
            throw new HairyException("ddfsdfd") 'System.OverflowException 
        Catch Ex as HairyException 
            messagebox.Show(ex.message)
        End Try
    End Sub
End Class


Public Class HairyException
    Inherits System.Exception

    Private _mStrException As String

    public overrides readonly property message as String
    Get        
        return _mStrException
    End Get
    End property

    Public sub new(ByRef strExcepMessage As String)
        _mStrException = strExcepMessage
    End Sub
End Class

But....

I want to more or less replace the Exception class - whatever the exception (not just a fat, hairy one). I wanted to more-or-less create a class which deals with the exception (format it into a nice string then print it to the windows event log, that kind of thing).

If I did another exception, say this:

throw new System.OverflowException
Catch Ex as HairyException

The HairyException class won't catch that...

[mendhak]

Since all exception classes derive from System.Exception, you could use Exception itself and work with its ex.message property.

So in the same code, this should work:

  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            Throw New HairyException("Holy cow!")

        Catch ex As Exception


            MessageBox.Show(ex.Message)

        End Try


    End Sub

See what I mean?

Now watch as I change its type to another exception thrown

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            Throw New System.IO.IOException("omg lololol")

        Catch ex As Exception

            MessageBox.Show(ex.Message)

        End Try


    End Sub

Still works.

Am I understanding what you want correctly?

[alex_read]

I was trying to go for this kind of scenario:

Catch Ex as HairyException
Ex.DoSomethingWithException()
End Try

This bit of code (from above), works fine for a throw Hairy error, but on any other type of error, only catching Ex as a standard .Net exception works.

Catch Ex as HairyException
messagebox.Show(ex.message)
End Try

Am I making any sense here?? I want a class to act exactly as though it were the .Net Exception class, but extended / with some extra functionality/methods added to it too...

Thanks so far btw!!

[mendhak]

Hmm... I don't think it can be done. Can you elaborate on what features you want to add?

[alex_read]

I just wanted to add a few routines to actually do something with the exception:

1) A function to build the exception properties into a nice, friendly error message with all the error info in.

2) Calls to other methods to log the error:
a) to a file
b) to a database
c) to the windows event log

[mendhak]

So what you want is an event logger. Create a class to which you can pass your error messages to, which will collect the error messages and write to a file or wherever you'd like.

So,

Try
'something
Catch sqlx as SqlException
EventLog.WriteEntry("An error occured.  The error is: " & sqlx.Message)
End Try

[Pirate]

Example for custom exception class:
http://www.dotnetspider.com/technolo...xceptions.aspx

[alex_read]

This is the kind of thing I'm after thanks (if anyone understands my dodgy attempt at a uml diagram)!!!

[mendhak]

If I've understood your diagram correctly, I think clsExceptionThrown should call clsLogging's write event.

[alex_read]

I should've maybe explained that too, sorry.

clsLogging would be a base class. Beneath it would be classes deriving this & overriding the ExecWriteEntry method - this could be a class which deals with writing to databases, a class which handles text &/or ini files, or (as in this 1st case) a class which deals with the windows event viewer making entries in that...

The clsExceptionThrown would provide a series of the "ExecWriteEntry" methods, with different arguments each time to call this routine in these classes derived from clsLogging.

I.e. I call:

Catch ex as clsException
    ex.ExecWriteEntry(intEventVwrEventId:=999)

This would create an instance of the EventVwr class & make a call to it's ExecWriteEntry method.

I call:

Catch ex as clsException
    ex.ExecWriteEntry(FileNameToWriteOut:="C:\Path\File.txt")

This could create an instance of the TextFile class & make a call to it's ExecWriteEntry method etc.

As a side note:
Those 2 " ExecLogError" labels on the left there should've read "ExecWriteEntry" instead! I've updated the above attachment!

[kleinma]

mendhak is basically correct with everything.. I see what you are trying to do, but the way the framework works, when an exception is thrown (by your code throwing one, or by the system encountering one) it will look for your catch statements and fire them in order, if you make your own exception class, you HAVE to throw it yourself. This is just how it works in .NET. The point of custom exceptions is to handle custom errors in your custom classes

what you COULD do perhaps is set up global error handling... (I haven't tested but I imagine that any local error handling would override the global handler... but this may be something you can use (the VB.NET code is towards the bottom)

http://dotnetjunkies.com/WebLog/mark...0/08/2152.aspx

[blakemckenna]

Kleinma,

Do you happen to have this C# Routine in VB.Net???

[JuggaloBrotha]

the vb code is at the bottom (as kleinma pointed out):

Here's how to get it done in VB.NET. First, create a class to intercept errors and call the ExceptionHandler.DisplayMessage() method.

Imports System
Imports System.ComponentModel
Imports System.Drawing
Imports System.Windows.Forms
Imports System.Threading
Imports Microsoft.VisualBasic

'The Error Handler class
'We need a class because event handling methods can't be static
Friend Class CustomExceptionHandler

'Handle the exception event
Public Sub OnThreadException(ByVal sender As Object, ByVal t As ThreadExceptionEventArgs)
Dim result As DialogResult = DialogResult.Cancel

Try
OurExceptionHandler.DisplayMessage(t.Exception)
Catch
Try
MessageBox.Show("Fatal Error", "Fatal Error", MessageBoxButtons.AbortRetryIgnore, MessageBoxIcon.Stop)
Finally
Application.Exit()
End Try
End Try
End Sub

Then hook it in the Main this way:

Public Class Main
'The application's main entry point.
Public Shared Sub Main()
'Explicitly set apartment state to Single Thread Apartment (STA)
'System.Threading.Thread.CurrentThread.ApartmentState = System.Threading.ApartmentState.STA
Dim eh As New CustomExceptionHandler
AddHandler Application.ThreadException, AddressOf eh.OnThreadException
Application.Run(New ErrorHandler)
End Sub
End Class

I hope some of you find this simple, yet elegant, solution as schweet as I did.

this actually made for a good read

[blakemckenna]

Thanks Jugga!!!