Raising errors in .NET

[Wokawidget]

VB6:

Dim objConn As Connection
On Error Goto ErrHandler:
 
   'code
 
   Exit Sub
ErrHandler:
   If Not (objConn Is Nothing) Then
      objConn.Close
      Set objConn = Nothing
   End If
   Err.Raise Err.Number, Err.Source, Err.Description

VB.NET

Dim Conn As SQLConnection
   Try
 
      'code
 
   Catch Ex As Exception
      If Not (Conn Is Nothing) Then
         Conn.Close
         Conn = Nothing
      End If
 
      'Want to raise exception to UI here
 
   End Try

How do I do this?

Woka

[mendhak]

Throw New Exception("DFKJ")

[wossname]

Throw New Exception("DFKJ")

Naughty froggy.

Throw New ApplicationException("DFKJ")

[kleinma]

woka... there is a try/catch example app in the 101 VB.NET examples

[kleinma]

also... unless your design model calls for a need to do it like that.. i would move any object disposing code and DB closing code to the finally clause.. so it is run if you error or not...

sort of like this

Public Sub DoFunThings()
        Dim CN As SqlConnection
        Dim CMD As SqlCommand
        Try
            CN = New SqlConnection(DBConnString)
            CN.Open()
            CMD = New SqlCommand("SELECT MARCLAR FROM MARCLAR WHERE [MARCLAR] = MARCLAR", CN)
            'PUT SOME CODE HERE THAT DO SOMETHING FUN
        Catch ex As SqlException
            'ERROR HANDLER HERE FOR DB ERROR
        Catch ex As Exception
            'ERROR HANDLER HERE FOR ANY OTHER
        Finally
            Try
                If Not CN Is Nothing Then
                    If CN.State <> ConnectionState.Closed Then
                        CN.Close()
                    End If
                    CN.Dispose()
                    CN = Nothing
                End If
                If Not CMD Is Nothing Then
                    CMD.Dispose()
                    CMD = Nothing
                End If
            Catch ex As Exception
            End Try
        End Try
    End Sub

[Shaggy Hiker]

Also, as you may have noticed, raising exceptions is more costly than vb6 error handling was. There is a noticeable pause prior to the catch block being caught. This makes raising your own errors a less appealing prospect.

When an exception is raised in .NET, I actually get to think "Gee, I wonder what it will be this time?" as I wait for the actual message to come up. I don't remember that long pause using On Error in vb6.

[kleinma]

I have only noticed that when in debug mode... or possibly on the first error raised in a release mode exe... other than that i see no lag in the error handling

[Shaggy Hiker]

I have only noticed that when in debug mode... or possibly on the first error raised in a release mode exe... other than that i see no lag in the error handling

I was wondering about that as I typed it. I, also, have only noticed that in debug mode, but I can't decide if that was because the lag was absent, reduced, or just because I was more attuned to it when in debug mode.

[RobDog888]

Naughty froggy.

Throw New ApplicationException("DFKJ")

It would depend on the severity of the exception Woka needs to throw.
If its a non-fatal error then mendhaks corrected example by wossname will be ok.
If its fatal then you need to use -

Throw New System.Exception("Connection Error!")' Or whatever you want to display.

[kleinma]

from MSDN

ApplicationException does not provide information as to the cause of the exception. In most scenarios, instances of this class should not be thrown. In cases where this class is instantiated, a human-readable message describing the error should be passed to the constructor.

[RobDog888]

Ah, that makes it even worse for the frog Time to return your MCAD Jk.

You can add the source and description properties of the exception for a useful error message.

Throw New System.Exception(ex.Source & " - " & ex.Message)

[kleinma]

Ah, that makes it even worse for the frog Time to return your MCAD Jk.

You can add the source and description properties of the exception for a useful error message.

Throw New System.Exception(ex.Source & " - " & ex.Message)

rob.. wouldn't that mean you would already have to have an exception if you are using the ex.source and ex.message?

Like

Try
    'something
Catch ex as system.exception
    Throw New System.Exception(ex.Source & " - " & ex.Message)
end try

i would think this would be just as good if your goal is to pass the exception up a level

Try
    'something
Catch ex as system.exception
    Throw ex
end try

[RobDog888]

I didnt realize that you could short hand it that way, but yes I was referring to your first example.

[WALDO]

I didnt realize that you could short hand it that way

Try
    'something
Catch ex As System.Exception
    Throw
End Try

[mendhak]

ApplicationWHAT?

It's no good because *I* say so.