Error Handling class?

[kto]

Hi there,
I am trying to write a simple error handling class and I can't seem to find any kind of samples on the web. I am catching the error like so...(errorhandling being my errorhandling class object)

    'class variables
    Dim errorString As String
    Dim exh As errorhandling

Public Sub....
.....'code
.......
        Catch ex As Exception
            trans.Rollback()
            exh = CType(context.Handler, errorhandling)
            'handle(ByVal ex as Exception) is the function which the ecception is passed to in the err handling class
            errorString = exh.handle(ex)
            Response.Redirect("Error.aspx?errorMsg=" & errorString)
        Finally
            If myConn.State = ConnectionState.Open Then
                myConn.Close()
            End If
            myConn = Nothing
        End Try

When I run it as is gives me a casting error with my ctype conversion...?? I can't even get into my error handling class to check if it works! Please, what am I missing here?

Another thing I'm trying to figure out is how I can access the specific error number? I know that Exceptions have a HResult() method but it's protected and I'm not sure how else I can access the values.

Any help on these issues would be most appreciated.
Cheers.

[Pirate]

Try this

Dim errorString As String
Dim exh As errorhandling
 
try 
 
 
        Catch ex As Exception
            trans.Rollback()
            exh = CType(context.Handler, errorhandling)
            'handle(ByVal ex as Exception) is the function which the ecception is passed to in the err handling class
            errorString = exh.handle(ex)
            Response.Redirect("Error.aspx?errorMsg=" & errorString)
'it should be here to catch the error if raised .
[B]catch x as execption [/B] 
 
            If myConn.State = ConnectionState.Open Then
                myConn.Close()
            End If
            myConn = Nothing
 
 
messagebox.show (x.message)

[kto]

On inserting that, it gets stuck when I try to call the handle() method in my error handling class:
(where errorString is a string looking for a return error string from the errorhandling class and exh is an instance of the errorhandling class)

errorString = exh.handle(ex)

...it gives me the error:

"Object reference not set to an instance of an object"

[Pirate]

Try this now :

try 
'Remove this and rebuild the try structure ! 
Catch ex As Exception
trans.Rollback()
exh = CType(context.Handler, errorhandling)
'handle(ByVal ex as Exception) is the function which the ecception is passed to in the err handling class
errorString = exh.handle(ex)
Response.Redirect("Error.aspx?errorMsg=" & errorString)
'it should be here to catch the error if raised .
catch x as execption  
 
Dim errorString As String
Dim exh As errorhandling
If myConn.State = ConnectionState.Open Then
myConn.Close()
End If
myConn = Nothing
 
messagebox.show (x.message)

[kto]

I'm so dozy I just forgot to instantiate the errorhandling class object. I have since done this and can now access the class...but I don't suppose you could point me in the right direction as to how I can access the error codes (I want to use a Select statement and firstly look for which exception occured and secondly, the different types of SQLExceptions etc.) and send back a manipulated string according to which kind of error it is?
Much thanks for your help.

[Pirate]

Oops .

For detailed info about generated errors , you can access different functions of the System.Exception class . Like :
Dim Exception as Exception

Exception.Stack
Exception.Source
Exception.Site
Exception.Message

then you can combine them all togother and show up a messagebox or write them to log file . Is this what you're asking about ?

[kto]

Not quite. I was under the impression that it was possible to get the associated error number of an error (just as a simple example...
[code]

Public Function handle(ByVal ex As Exception)
Dim exNo As Integer

Select Case exNo
Case 111
if exno = 1
Return "An SQL Exception has occured. Type:"
Case 222
Return "An IO Exceptoion has occured. Type:"
Case Else
s = ex.ToString
Return s
End Select

End Function

[Pirate]

As far as I know , there is no associated number with exception error in .NET .

[kto]

Not quite. I was under the impression that it was possible to get the associated error number of an error.
An example of the idea I'm trying to work out...

    Public Function handle(ByVal ex As Exception)
        Dim exNo As Integer
        Dim s As String
        exNo = ex.HResult()
        s = ex.ToString

        Select Case exNo
            Case 111
                If exNo = 1 Then
                    Return "An SQL Null Value Exception has occured. Type:" & s
                ElseIf exNo = 2 Then
                    Return "An SQL Exception has occured. Type:" & s
                End If

            Case 222
                Return "An IO Exception has occured. Type:" & s

            Case Else
                s = ex.ToString
                Return s
        End Select

    End Function

But HResult is a protected method of the Exception class...is there not some way I can access this to find out the specific error numbers?

[Pirate]

Since you are working on handling specific exception "SQL Exception" , why don't you use it instead of the generic exception class ? Like this :

This gets the error number I guess .

Catch ex As SqlClient.SqlException
MessageBox.Show(ex.Number())

and so on .

[kto]

because I don't know what type of error has occured until it reaches my errorhandling class!

Basically I want to catch whatever error occurs, pass it to a my errorhandling class, figure out what type it is and return an appropriate string back to where the error occured.

How can I figure out what type of error has occured?

[VBCrazyCoder]

SQLExceptions have associated error numbers. For example, error number 229 is a permissions error. You can access it by myException.Number where myException is a SQLException. Regular Exception types don't have a number associated.

I also trap specific SQL Exception Numbers in some of my code to take the appropriate action. Works well for me!

[Pirate]

Originally posted by kto
How can I figure out what type of error has occured?

Call this little sub to see what type of exception it's going to throw . This is one way .

Private Sub callme()
        Dim errortype As String
        Dim ex As Exception
 
        Try
            Dim a As Integer = "aaaa"
 
        Catch ex 
            'here you can figure out what error was generated 
            'simply by converting exception type to 
            'string 
            errortype = ex.GetType().ToString
            MessageBox.Show(errortype.ToString)
 
        End Try
 
    End Sub

[Pirate]

This is the other way . It uses GetType

Private Sub callme()
        Dim errortype As String
        Dim ex As Exception
 
        Try
            Dim a As Integer = "aaaa"
 
        Catch ex
 
        End Try
 
 
        'here you have to list exceptions that are expect to be thrown 
        'in this way . 
        If ex.GetType Is GetType(InvalidCastException) Then
 
            MsgBox("Error Type " & ex.Message & "Do whatever here ")
 
        ElseIf ex.GetType Is GetType(ExecutionEngineException) Then
            'do your code here 
 
        ElseIf ex.GetType Is GetType(InvalidProgramException) Then
            'do your code here 
 
        End If
    End Sub

[kto]

cheers mate, you've made this wee Irish lass very happy!